diff --git a/Mamesaver/BlankScreen.cs b/Mamesaver/BlankScreen.cs
index 69dea49..52cddf6 100644
--- a/Mamesaver/BlankScreen.cs
+++ b/Mamesaver/BlankScreen.cs
@@ -10,7 +10,7 @@
 
 namespace Mamesaver
 {
-    internal class BlankScreen
+    internal class BlankScreen : IDisposable
     {
         private readonly PowerManager _powerManager;
         public BackgroundForm BackgroundForm { get; }
@@ -96,5 +96,21 @@ private void ReleaseDeviceContext()
                 Log.Error(ex, "Error releasing device context for {screen}", Screen.DeviceName);
             }
         }
+
+        public void Dispose()
+        {
+            Dispose(true);
+            GC.SuppressFinalize(this);
+       }
+
+        protected virtual void Dispose(bool disposing)
+        {
+            if (!disposing) return;
+
+            _powerManager?.Dispose();
+            BackgroundForm?.Dispose();
+        }
+
+        ~BlankScreen() => Dispose(false);
     }
 }
\ No newline at end of file
diff --git a/Mamesaver/CaptureScreen.cs b/Mamesaver/CaptureScreen.cs
index 5dbe190..b20d39f 100644
--- a/Mamesaver/CaptureScreen.cs
+++ b/Mamesaver/CaptureScreen.cs
@@ -33,7 +33,7 @@ public void Dispose()
             GC.SuppressFinalize(this);
         }
 
-        public virtual void Dispose(bool disposing) => ReleaseUnmanagedResources();
+        protected virtual void Dispose(bool disposing) => ReleaseUnmanagedResources();
         ~CaptureScreen() => Dispose(false);
 
         private void ReleaseUnmanagedResources()
diff --git a/Mamesaver/GamePlayManager.cs b/Mamesaver/GamePlayManager.cs
index 79a7c4f..d8c3e81 100644
--- a/Mamesaver/GamePlayManager.cs
+++ b/Mamesaver/GamePlayManager.cs
@@ -26,9 +26,9 @@ internal class GamePlayManager : IDisposable
         private readonly PowerManager _powerManager;
         private readonly MameInvoker _invoker;
 
-        public delegate void PlayGameEventHandler(object sender, EventArgs args);
-        public delegate void StartGameEventHandler(object sender, EventArgs args);
-        public delegate void GameStartedEventHandler(object sender, EventArgs args);
+        public delegate void PlayGameEventHandler(object sender, EventArgs e);
+        public delegate void StartGameEventHandler(object sender, EventArgs e);
+        public delegate void GameStartedEventHandler(object sender, EventArgs e);
 
         /// <summary>
         ///     Game has been started by MAME.
@@ -139,7 +139,7 @@ private void PreviousGame()
         }
 
         /// <summary>
-        ///     Deselects a game, saving configuration and playing the next game
+        ///     Deselects a game, saving configuration and playing the next game.
         /// </summary>
         private void DeselectGame(Game game)
         {
diff --git a/Mamesaver/MameScreen.cs b/Mamesaver/MameScreen.cs
index 10d1541..140e03d 100644
--- a/Mamesaver/MameScreen.cs
+++ b/Mamesaver/MameScreen.cs
@@ -12,7 +12,7 @@ namespace Mamesaver
     ///     A screen that will launch MAME with a random game from the list. If configured, this screen also handles hotkey events which
     ///     affect the MAME process.
     /// </summary>
-    internal class MameScreen : BlankScreen, IDisposable
+    internal class MameScreen : BlankScreen
     {
         private readonly Settings _settings;
         private readonly GamePlayManager _gamePlayManager;
@@ -163,8 +163,10 @@ private void GameTimerTick(object sender, EventArgs e)
         ///     Stop the timer, set cancelled flag, close any current process and close the background form.
         ///     Once this has all been done, the application should end.
         /// </summary>
-        public virtual void Dispose(bool disposing)
+        protected override void Dispose(bool disposing)
         {
+            base.Dispose(disposing);
+
             if (!disposing || !_initialised) return;
 
             Log.Information("Closing primary MAME screen {screen}", Screen.DeviceName);
@@ -187,12 +189,6 @@ private void DisposeTimers()
             _gameTimer = _splashTimer = null;
         }
 
-        public void Dispose()
-        {
-            Dispose(true);
-            GC.SuppressFinalize(this);
-        }
-
         ~MameScreen() => Dispose(false);
     }
 }
\ No newline at end of file
diff --git a/Mamesaver/Power/PowerEventWatcher.cs b/Mamesaver/Power/PowerEventWatcher.cs
index 1d06f38..3adfd34 100644
--- a/Mamesaver/Power/PowerEventWatcher.cs
+++ b/Mamesaver/Power/PowerEventWatcher.cs
@@ -8,7 +8,7 @@ namespace Mamesaver.Power
     ///     Listens for power source change events, firing a <see cref="PowerStateChanged"/> event
     ///     if received.
     /// </summary>
-    public class PowerEventWatcher
+    public class PowerEventWatcher : IDisposable
     {
         /// <summary>
         ///     Value of event corresponding to a power state change.
@@ -21,7 +21,7 @@ public class PowerEventWatcher
         private ManagementEventWatcher _managementEventWatcher;
         public event PowerEventHandler PowerStateChanged;
 
-        public delegate void PowerEventHandler(object sender, EventArgs args);
+        public delegate void PowerEventHandler(object sender, EventArgs e);
 
         /// <summary>
         ///     Initialises the power event watcher to fire <see cref="PowerStateChanged"/>
@@ -51,7 +51,7 @@ private void PowerEventArrived(object sender, EventArrivedEventArgs args)
             }
         }
 
-        public virtual void Dispose(bool disposing)
+        protected virtual void Dispose(bool disposing)
         {
             if (!disposing) return;
 
diff --git a/Mamesaver/Power/PowerManager.cs b/Mamesaver/Power/PowerManager.cs
index bc62715..3c25e05 100644
--- a/Mamesaver/Power/PowerManager.cs
+++ b/Mamesaver/Power/PowerManager.cs
@@ -21,7 +21,7 @@ public class PowerManager : IDisposable
         private readonly PowerEventWatcher _eventWatcher;
         private Timer _sleepTimer;
 
-        public delegate void SleepTriggerManager(object sender, EventArgs args);
+        public delegate void SleepTriggerManager(object sender, EventArgs e);
 
         /// <summary>
         ///     Fired when the screensaver should turn the display to sleep.
@@ -32,7 +32,7 @@ public class PowerManager : IDisposable
         ///     Time before a <see cref="SleepTriggered"/> event is published, based on the user's power management 
         ///     configuration.
         /// </summary>
-        private TimeSpan _sleepTimeout;
+        private TimeSpan? _sleepTimeout;
 
         /// <summary>
         ///     Current power source type.
@@ -72,24 +72,43 @@ public void Initialise()
 
             // Identify policy for selected power type
             _sleepTimeout = GetSleepTimeout(powerType.Value);
-            Log.Information("Connected to {powerType} power; sleeping after {min} minutes", 
-                powerType.Value.ToString(), _sleepTimeout.TotalMinutes);
-
-            // Create a timer which fires once when the display or computer should go to sleep
-            _sleepTimer = new Timer { Interval = Math.Min(_sleepTimeout.TotalMilliseconds, int.MaxValue), AutoReset = false };
-
-            _sleepTimer.Elapsed += SleepTimerTick;
-            _sleepTimer.Start();
+            if (_sleepTimeout == null)
+            {
+                Log.Information("Connected to {powerType} power; no sleep configured", powerType.Value.ToString());
+            }
+            else
+            {
+                // Create a timer which fires once when the display or computer should go to sleep
+                Log.Information("Connected to {powerType} power; sleeping after {min} minutes", powerType.Value.ToString(), _sleepTimeout.Value.TotalMinutes);
+                InitSleepTimer();
+            }
 
             // Receive notifications for power state changes so the timer can be updated
             _eventWatcher.Initialise();
             _eventWatcher.PowerStateChanged += PowerStateChanged;
         }
 
+        /// <summary>
+        ///     Either creates or updates the sleep timer.
+        /// </summary>
+        private void InitSleepTimer()
+        {
+            if (_sleepTimeout == null) throw new InvalidOperationException("Can't create a timer with no timeout specified");
+
+            if (_sleepTimer == null)
+            {
+                _sleepTimer = new Timer { AutoReset = false };
+                _sleepTimer.Elapsed += SleepTimerTick;
+            }
+
+            _sleepTimer.Interval = (int)_sleepTimeout.Value.TotalMilliseconds;
+            _sleepTimer.Start();
+        }
+
         /// <summary>
         ///     Returns the lowest of screen and PC sleep settings for a given power type.
         /// </summary>
-        private static TimeSpan GetSleepTimeout(PowerType powerType)
+        private static TimeSpan? GetSleepTimeout(PowerType powerType)
         {
             var powerPolicy = PowerInterop.GetPowerPolicy(powerType);
             return new[] { powerPolicy.VideoTimeout, powerPolicy.IdleTimeout }.Min();
@@ -119,16 +138,20 @@ private void PowerStateChanged(object sender, EventArgs args)
             if (_currentPowerType == powerType) return;
             _currentPowerType = powerType.Value;
 
+            _sleepTimer?.Stop();
+
             // Identify policy for selected power type
             _sleepTimeout = GetSleepTimeout(powerType.Value);
-            Log.Information("Power changed to {powerType} power; sleeping after {min} minutes",
-                powerType.Value.ToString(), _sleepTimeout.TotalMinutes);
-
-            // Update sleep timer on power state change due to different sleep configurations
-            _sleepTimer.Interval = Math.Min(_sleepTimeout.TotalMilliseconds, int.MaxValue);
-
-            _sleepTimer.Stop();
-            _sleepTimer.Start();
+            if (_sleepTimeout == null)
+            {
+                Log.Information("Power changed to {powerType} power; no sleep configured", powerType.Value.ToString());
+            }
+            else
+            {
+                // Update sleep timer on power state change due to different sleep configurations
+                Log.Information("Power changed to {powerType} power; sleeping after {min} minutes", powerType.Value.ToString(), _sleepTimeout.Value.TotalMinutes);
+                InitSleepTimer();
+            }
         }
 
         /// <summary>
@@ -142,7 +165,7 @@ public void Dispose()
             GC.SuppressFinalize(this);
         }
 
-        public virtual void Dispose(bool disposing)
+        protected virtual void Dispose(bool disposing)
         {
             if (!disposing) return;
             _sleepTimer?.Dispose();
diff --git a/Mamesaver/Windows/PlatformInvokeGDI32.cs b/Mamesaver/Windows/PlatformInvokeGDI32.cs
index 10aba38..bb0b2e1 100644
--- a/Mamesaver/Windows/PlatformInvokeGDI32.cs
+++ b/Mamesaver/Windows/PlatformInvokeGDI32.cs
@@ -4,38 +4,38 @@
 
 namespace Mamesaver.Windows
 {
-    public class PlatformInvokeGdi32
+    internal class PlatformInvokeGdi32
     {
-        public const int SRCOPY = 13369376;
+        internal const int SRCOPY = 13369376;
 
         [DllImport("gdi32.dll", EntryPoint = "DeleteDC")]
-        public static extern IntPtr DeleteDC(IntPtr hDc);
+        internal static extern IntPtr DeleteDC(IntPtr hDc);
 
         [DllImport("gdi32.dll", EntryPoint = "DeleteObject")]
-        public static extern IntPtr DeleteObject(IntPtr hDc);
+        internal static extern IntPtr DeleteObject(IntPtr hDc);
 
         [DllImport("gdi32.dll", EntryPoint = "BitBlt")]
-        public static extern bool BitBlt(IntPtr hdcDest, int xDest, int yDest, int wDest, int hDest, IntPtr hdcSource, int xSrc, int ySrc, int rasterOp);
+        internal static extern bool BitBlt(IntPtr hdcDest, int xDest, int yDest, int wDest, int hDest, IntPtr hdcSource, int xSrc, int ySrc, int rasterOp);
 
         [DllImport("gdi32.dll", EntryPoint = "StretchBlt")]
-        public static extern bool StretchBlt(IntPtr hdcDest, int xDest, int yDest, int wDest, int hDest, IntPtr hdcSource, int xSrc, int ySrc, int wSrc, int hSrc, int RasterOp);
+        internal static extern bool StretchBlt(IntPtr hdcDest, int xDest, int yDest, int wDest, int hDest, IntPtr hdcSource, int xSrc, int ySrc, int wSrc, int hSrc, int RasterOp);
 
         [DllImport("gdi32.dll")]
-        public static extern IntPtr CreateCompatibleDC(IntPtr hdc);
+        internal static extern IntPtr CreateCompatibleDC(IntPtr hdc);
 
         [DllImport("gdi32.dll")]
-        public static extern IntPtr CreateCompatibleBitmap(IntPtr hdc, int nWidth, int nHeight);
+        internal static extern IntPtr CreateCompatibleBitmap(IntPtr hdc, int nWidth, int nHeight);
 
         [DllImport("gdi32.dll", EntryPoint = "SelectObject")]
-        public static extern IntPtr SelectObject(IntPtr hdc, IntPtr bmp);
+        internal static extern IntPtr SelectObject(IntPtr hdc, IntPtr bmp);
 
         [DllImport("gdi32.dll", CharSet = CharSet.Auto, SetLastError = true, ExactSpelling = true)]
-        public static extern int GetDeviceCaps(IntPtr hDC, int nIndex);
+        internal static extern int GetDeviceCaps(IntPtr hDC, int nIndex);
 
         /// <summary>
         /// DeviceCap - Device capabilities
         /// </summary>
-        public enum DeviceCap
+        internal enum DeviceCap
         {
             /// <summary>
             /// Logical pixels inch in X
diff --git a/Mamesaver/Windows/PlatformInvokeUSER32.cs b/Mamesaver/Windows/PlatformInvokeUSER32.cs
index 4d94ac3..d539329 100644
--- a/Mamesaver/Windows/PlatformInvokeUSER32.cs
+++ b/Mamesaver/Windows/PlatformInvokeUSER32.cs
@@ -4,51 +4,51 @@
 
 namespace Mamesaver.Windows
 {
-    public class PlatformInvokeUser32
+    internal class PlatformInvokeUser32
     {
-        public const int SM_CXSCREEN = 0;
-        public const int SM_CYSCREEN = 1;
-        public const int SW_MINIMIZE = 6;
+        internal const int SM_CXSCREEN = 0;
+        internal const int SM_CYSCREEN = 1;
+        internal const int SW_MINIMIZE = 6;
 
         [DllImport("user32.dll", CharSet = CharSet.Auto)]
-        public static extern IntPtr SendMessage(IntPtr hWnd, int Msg, int wParam, IntPtr lParam);
+        internal static extern IntPtr SendMessage(IntPtr hWnd, int Msg, int wParam, IntPtr lParam);
 
         [DllImport("user32.dll")]
-        public static extern void SetWindowPos(IntPtr hwnd, IntPtr hwndInsertAfter, int x, int y, int width, int height, uint flags);
+        internal static extern void SetWindowPos(IntPtr hwnd, IntPtr hwndInsertAfter, int x, int y, int width, int height, uint flags);
 
         [DllImport("user32.dll", EntryPoint = "GetDesktopWindow")]
-        public static extern IntPtr GetDesktopWindow();
+        internal static extern IntPtr GetDesktopWindow();
 
         [DllImport("user32.dll", EntryPoint = "GetDC")]
-        public static extern IntPtr GetDC(IntPtr ptr);
+        internal static extern IntPtr GetDC(IntPtr ptr);
 
         [DllImport("user32.dll", EntryPoint = "GetSystemMetrics")]
-        public static extern int GetSystemMetrics(int abc);
+        internal static extern int GetSystemMetrics(int abc);
 
         [DllImport("user32.dll", EntryPoint = "GetWindowDC")]
-        public static extern IntPtr GetWindowDC(Int32 ptr);
+        internal static extern IntPtr GetWindowDC(Int32 ptr);
 
         [DllImport("user32.dll", EntryPoint = "ReleaseDC")]
-        public static extern IntPtr ReleaseDC(IntPtr hWnd, IntPtr hDC);
+        internal static extern IntPtr ReleaseDC(IntPtr hWnd, IntPtr hDC);
 
         [DllImport("user32.dll")]
         [return: MarshalAs(UnmanagedType.Bool)]
-        public static extern bool GetWindowRect(IntPtr hWnd, out RECT lpRect);
+        internal static extern bool GetWindowRect(IntPtr hWnd, out RECT lpRect);
 
         [DllImport("user32.dll")]
         [return: MarshalAs(UnmanagedType.Bool)]
-        public static extern bool ShowWindow(IntPtr hWnd, int nCmdShow);
+        internal static extern bool ShowWindow(IntPtr hWnd, int nCmdShow);
 
         [StructLayout(LayoutKind.Sequential)]
-        public struct RECT
+        internal struct RECT
         {
-            public int Left;        // x position of upper-left corner
-            public int Top;         // y position of upper-left corner
-            public int Right;       // x position of lower-right corner
-            public int Bottom;      // y position of lower-right corner
+            internal int Left;        // x position of upper-left corner
+            internal int Top;         // y position of upper-left corner
+            internal int Right;       // x position of lower-right corner
+            internal int Bottom;      // y position of lower-right corner
         }
 
         [DllImport("user32.dll")]
-        public static extern bool SetProcessDPIAware();
+        internal static extern bool SetProcessDPIAware();
     }
 }
diff --git a/Mamesaver/Windows/PowerInterop.cs b/Mamesaver/Windows/PowerInterop.cs
index af23e4f..7eb333f 100644
--- a/Mamesaver/Windows/PowerInterop.cs
+++ b/Mamesaver/Windows/PowerInterop.cs
@@ -37,10 +37,10 @@ public static PowerPolicy GetPowerPolicy(PowerType powerType)
                     {
                         IdleTimeout =
                             userPolicy.IdleTimeoutAc == 0 || userPolicy.IdleAc.Action == POWER_ACTION.PowerActionNone
-                                ? TimeSpan.MaxValue
+                                ? (TimeSpan?)null
                                 : TimeSpan.FromSeconds(userPolicy.IdleTimeoutAc),
                         VideoTimeout = userPolicy.VideoTimeoutAc == 0
-                            ? TimeSpan.MaxValue
+                            ? (TimeSpan?)null
                             : TimeSpan.FromSeconds(userPolicy.VideoTimeoutAc)
                     };
                 case PowerType.DC:
@@ -48,10 +48,10 @@ public static PowerPolicy GetPowerPolicy(PowerType powerType)
                     {
                         IdleTimeout =
                             userPolicy.IdleTimeoutDc == 0 || userPolicy.IdleDc.Action == POWER_ACTION.PowerActionNone
-                                ? TimeSpan.MaxValue
+                                ? (TimeSpan?)null
                                 : TimeSpan.FromSeconds(userPolicy.IdleTimeoutDc),
                         VideoTimeout = userPolicy.VideoTimeoutDc == 0
-                            ? TimeSpan.MaxValue
+                            ? (TimeSpan?)null
                             : TimeSpan.FromSeconds(userPolicy.VideoTimeoutDc)
                     };
                 default:
@@ -68,7 +68,14 @@ public enum PowerType
 
     public class PowerPolicy
     {
-        public TimeSpan VideoTimeout { get; set; }
-        public TimeSpan IdleTimeout { get; set; }
+        /// <summary>
+        ///     Timeout for screen to go to sleep, or <c>null</c> if no sleep is specified.
+        /// </summary>
+        public TimeSpan? VideoTimeout { get; set; }
+
+        /// <summary>
+        ///     Timeout for PC to go to sleep, or <c>null</c> if no sleep is specified.
+        /// </summary>
+        public TimeSpan? IdleTimeout { get; set; }
     }
 }
\ No newline at end of file
diff --git a/Mamesaver/Windows/UserActivityHook.cs b/Mamesaver/Windows/UserActivityHook.cs
index 233b6b7..b828907 100644
--- a/Mamesaver/Windows/UserActivityHook.cs
+++ b/Mamesaver/Windows/UserActivityHook.cs
@@ -479,19 +479,20 @@ public UserActivityHook(bool InstallMouseHook, bool InstallKeyboardHook)
             Start(InstallMouseHook, InstallKeyboardHook);
         }
 
-        protected virtual void Dispose(bool disposing)
-        {
-            if (disposing)
-            {
-                Stop(true, true, false);
-            }
-        }
         public void Dispose()
         {
             Dispose(true);
             GC.SuppressFinalize(this);
         }
 
+        protected virtual void Dispose(bool disposing)
+        {
+            if (!disposing) return;
+
+            Stop(true, true, false);
+        }
+
+    
         ~UserActivityHook() => Dispose(false);
 
         /// <summary>