Core code for VB.NET:

Namespace PDA

    Public Class Video

        Private Const SETPOWERMANAGEMENT As Int32 = 6147

        Declare Function ExtEscapeSet Lib "coredll" Alias "ExtEscape" (ByVal hdc As IntPtr, _

                                                  ByVal nEscape As Int32, _

                                                  ByVal cbInput As Int32, _

                                                  ByVal plszInData As Byte(), _

                                                  ByVal cbOutput As Int32, _

                                                  ByVal lpszOutData As IntPtr) As Int32

        Declare Function GetDC Lib "coredll" (ByVal hwnd As IntPtr) As IntPtr

        Public Enum VideoPowerState As Integer

            VideoPowerOn = 1

            VideoPowerStandBy

            VideoPowerSuspend

            VideoPowerOff

        End Enum

        Public Shared Sub PowerOff()

            Dim hdc As IntPtr = GetDC(IntPtr.Zero)

            Dim vpm() As Byte = {12, 0, 0, 0, 1, 0, 0, 0, VideoPowerState.VideoPowerOff, 0, 0, 0, 0}

            ExtEscapeSet(hdc, SETPOWERMANAGEMENT, 12, vpm, 0, IntPtr.Zero)

        End Sub

        Public Shared Sub PowerOn()

            Dim hdc As IntPtr = GetDC(IntPtr.Zero)

            Dim vpm() As Byte = {12, 0, 0, 0, 1, 0, 0, 0, VideoPowerState.VideoPowerOn, 0, 0, 0, 0}

            ExtEscapeSet(hdc, SETPOWERMANAGEMENT, 12, vpm, 0, IntPtr.Zero)

        End Sub

    End Class

End Namespace

Core code for C#

using System;

using System.Runtime.InteropServices;

namespace OpenNETCF

{

/// <summary>

/// Summary description for Video.

/// </summary>

public class Video

{

        // GDI Escapes for ExtEscape()

        private const uint QUERYESCSUPPORT   = 8;

        // The following are unique to CE

        private const uint GETVFRAMEPHYSICAL =  6144;

        private const uint GETVFRAMELEN   = 6145;

        private const uint DBGDRIVERSTAT   = 6146;

        private const uint SETPOWERMANAGEMENT =  6147;

        private const uint GETPOWERMANAGEMENT =  6148;

        public static void PowerOff()

        {

               IntPtr hdc = GetDC(IntPtr.Zero);

               uint func = SETPOWERMANAGEMENT;

               uint size = 12;

               byte[] vpm = new byte[size];

               //structure size

               BitConverter.GetBytes(size).CopyTo(vpm, 0);

               //dpms version

               BitConverter.GetBytes(0x0001).CopyTo(vpm, 4);

               //power state

               BitConverter.GetBytes((uint)VideoPowerState.VideoPowerOff).CopyTo(vpm, 8);

               ExtEscapeSet(hdc, SETPOWERMANAGEMENT, size, vpm, 0, IntPtr.Zero);

        }

        public static void PowerOn()

        {

        IntPtr hdc = GetDC(IntPtr.Zero);

               uint size = 12;

               byte[] vpm = new byte[size];

               //structure size

               BitConverter.GetBytes(size).CopyTo(vpm, 0);

               //dpms version

               BitConverter.GetBytes(0x0001).CopyTo(vpm, 4);

               //power state

               BitConverter.GetBytes((uint)VideoPowerState.VideoPowerOn).CopyTo(vpm, 8);

               ExtEscapeSet(hdc, SETPOWERMANAGEMENT, size, vpm, 0, IntPtr.Zero);

               }

        [DllImport("coredll", EntryPoint="ExtEscape")]

        private static extern int ExtEscapeSet(

               IntPtr hdc,

               uint nEscape,

               uint cbInput,

               byte[] lpszInData,

               int cbOutput,

               IntPtr lpszOutData

               );

        [DllImport("coredll")]

        private static extern IntPtr GetDC(IntPtr hwnd);

}

public enum VideoPowerState : uint

{

        VideoPowerOn = 1,

        VideoPowerStandBy,

        VideoPowerSuspend,

        VideoPowerOff

}