Events fired when the display power is switched On/Off

I search for an event or if doesn't exist, a method to know if the screen off (Power Options – Control Panel - Turn off the display setting).

None of these solutions work for me.
So either I was wrong somewhere, or it's just not suitable.

How to get the events when the screen/display goes to power OFF or ON?

I expect some track or solution.
The problem is that I don't know what I'm doing, if you could help me a little more it would be cool.

I made this, but it doesn't work:

internal static class NativeMethods
{
    public static Guid GUID_MONITOR_POWER_ON = new Guid(0x02731015, 0x4510, 0x4526, 0x99, 0xE6, 0xE5, 0xA1, 0x7E, 0xBD, 0x1A, 0xEA);
    public const int DEVICE_NOTIFY_WINDOW_HANDLE = 0x00000000;
    public const int WM_POWERBROADCAST = 0x0218;
    public const int PBT_POWERSETTINGCHANGE = 0x8013;

    [StructLayout(LayoutKind.Sequential, Pack = 4)]
    public struct POWERBROADCAST_SETTING
    {
        public Guid PowerSetting;
        public uint DataLength;
        public byte Data;
    }

    [DllImport(@"User32", SetLastError = true, EntryPoint = "RegisterPowerSettingNotification", CallingConvention = CallingConvention.StdCall)]
    public static extern IntPtr RegisterPowerSettingNotification(IntPtr hRecipient, ref Guid PowerSettingGuid, Int32 Flags);

    [DllImport(@"User32", SetLastError = true, EntryPoint = "UnregisterPowerSettingNotification", CallingConvention = CallingConvention.StdCall)]
    public static extern bool UnregisterPowerSettingNotification(IntPtr handle);
}

private void WndProc(IntPtr hwnd, int msg, IntPtr wParam, IntPtr lParam, ref bool handled)
{
    Debug.WriteLine("EVENT", "DEBUG");
}

public form1()
{
    NativeMethods.RegisterPowerSettingNotification(this.Handle, ref NativeMethods.GUID_MONITOR_POWER_ON, NativeMethods.DEVICE_NOTIFY_WINDOW_HANDLE);
}

The declarations are mostly correct, you just need to handle the messages when you're notified.

Override OnHandleCreated, to be sure that the Window handle is valid when you pass it to the function.
Override WndProc, to receive and process the WM_POWERBROADCAST event. Note that the Guid used in Windows 8+ is different from the one used in Window 7. Not much, in Windows 8+ is also available a POWERBROADCAST_SETTING.Data value of 0x02, including the Monitor Dimmed status; anyway, it's recommended that you use this Guid instead.
You can check the OSVersion before calling RegisterPowerSettingNotification.
This function returns a handle (IntPtr), which is used to call UnregisterPowerSettingNotification after.

The first notification is sent as soon as your application begins to process the messages (you should receive a message informing you that the Monitor is On :).
Note that these events are notified when the System turns On/Off or dims the Display power, not if you switch the Monitor's Power button On/Off.

public partial class Form1 : Form
{
    private IntPtr unRegPowerNotify = IntPtr.Zero;

    protected override void OnHandleCreated(EventArgs e)
    {
        base.OnHandleCreated(e);
        var settingGuid = new NativeMethods.PowerSettingGuid();
        Guid powerGuid = IsWindows8Plus()
                       ? settingGuid.ConsoleDisplayState 
                       : settingGuid.MonitorPowerGuid;

        unRegPowerNotify = NativeMethods.RegisterPowerSettingNotification(
            this.Handle, powerGuid, NativeMethods.DEVICE_NOTIFY_WINDOW_HANDLE);
    }

    private bool IsWindows8Plus()
    {
        var version = Environment.OSVersion.Version;
        if (version.Major > 6) return true; // Windows 10+
        if (version.Major == 6 && version.Minor > 1) return true; // Windows 8+
        return false;  // Windows 7 or less
    }

    protected override void WndProc(ref Message m)
    {
        switch (m.Msg) {
            case NativeMethods.WM_POWERBROADCAST:
                if (m.WParam == (IntPtr)NativeMethods.PBT_POWERSETTINGCHANGE)
                {
                    var settings = (NativeMethods.POWERBROADCAST_SETTING)m.GetLParam(
                        typeof(NativeMethods.POWERBROADCAST_SETTING));
                    switch (settings.Data) {
                        case 0:
                            Console.WriteLine("Monitor Power Off");
                            break;
                        case 1:
                            Console.WriteLine("Monitor Power On");
                            break;
                        case 2:
                            Console.WriteLine("Monitor Dimmed");
                            break;
                    }
                }
                m.Result = (IntPtr)1;
                break;
        }
        base.WndProc(ref m);
    }

    protected override void OnFormClosing(FormClosingEventArgs e)
    {
        NativeMethods.UnregisterPowerSettingNotification(unRegPowerNotify);
        base.OnFormClosing(e);
    }
}

NativeMethods declarations:

using System.Runtime.InteropServices;

class NativeMethods
{
    internal const uint DEVICE_NOTIFY_WINDOW_HANDLE = 0x0;
    internal const uint DEVICE_NOTIFY_SERVICE_HANDLE = 0x1;
    internal const int WM_POWERBROADCAST = 0x0218;
    internal const int PBT_POWERSETTINGCHANGE = 0x8013;

    [DllImport("User32.dll", SetLastError = true)]
    internal static extern IntPtr RegisterPowerSettingNotification(IntPtr hWnd, [In] Guid PowerSettingGuid, uint Flags);

    [DllImport("User32.dll", SetLastError = true)]
    internal static extern bool UnregisterPowerSettingNotification(IntPtr hWnd);

    [StructLayout(LayoutKind.Sequential, Pack = 4)]
    internal struct POWERBROADCAST_SETTING
    {
        public Guid PowerSetting;
        public uint DataLength;
        public byte Data;
    }

    // https://docs.microsoft.com/en-us/windows/win32/power/power-setting-guids
    public class PowerSettingGuid
    {
        // 0=Powered by AC, 1=Powered by Battery, 2=Powered by short-term source (UPC)
        public Guid AcdcPowerSource { get; } = new Guid("5d3e9a59-e9D5-4b00-a6bd-ff34ff516548");
        // POWERBROADCAST_SETTING.Data = 1-100
        public Guid BatteryPercentageRemaining { get; } = new Guid("a7ad8041-b45a-4cae-87a3-eecbb468a9e1");
        // Windows 8+: 0=Monitor Off, 1=Monitor On, 2=Monitor Dimmed
        public Guid ConsoleDisplayState { get; } = new Guid("6fe69556-704a-47a0-8f24-c28d936fda47");
        // Windows 8+, Session 0 enabled: 0=User providing Input, 2=User Idle
        public Guid GlobalUserPresence { get; } = new Guid("786E8A1D-B427-4344-9207-09E70BDCBEA9");
        // 0=Monitor Off, 1=Monitor On.
        public Guid MonitorPowerGuid { get; } = new Guid("02731015-4510-4526-99e6-e5a17ebd1aea");
        // 0=Battery Saver Off, 1=Battery Saver On.
        public Guid PowerSavingStatus { get; } = new Guid("E00958C0-C213-4ACE-AC77-FECCED2EEEA5");

        // Windows 8+: 0=Off, 1=On, 2=Dimmed
        public Guid SessionDisplayStatus { get; } = new Guid("2B84C20E-AD23-4ddf-93DB-05FFBD7EFCA5");

        // Windows 8+, no Session 0: 0=User providing Input, 2=User Idle
        public Guid SessionUserPresence { get; } = new Guid("3C0F4548-C03F-4c4d-B9F2-237EDE686376");
        // 0=Exiting away mode 1=Entering away mode
        public Guid SystemAwaymode { get; } = new Guid("98a7f580-01f7-48aa-9c0f-44352c29e5C0");

        /* Windows 8+ */
        // POWERBROADCAST_SETTING.Data not used
        public Guid IdleBackgroundTask { get; } = new Guid(0x515C31D8, 0xF734, 0x163D, 0xA0, 0xFD, 0x11, 0xA0, 0x8C, 0x91, 0xE8, 0xF1);

        public Guid PowerSchemePersonality { get; } = new Guid(0x245D8541, 0x3943, 0x4422, 0xB0, 0x25, 0x13, 0xA7, 0x84, 0xF6, 0x79, 0xB7);

        // The Following 3 Guids are the POWERBROADCAST_SETTING.Data result of PowerSchemePersonality
        public Guid MinPowerSavings { get; } = new Guid("8c5e7fda-e8bf-4a96-9a85-a6e23a8c635c");
        public Guid MaxPowerSavings { get; } = new Guid("a1841308-3541-4fab-bc81-f71556f20b4a");
        public Guid TypicalPowerSavings { get; } = new Guid("381b4222-f694-41f0-9685-ff5bb260df2e");
    }

}