You should try this one instead:
(Add-Type '[DllImport("user32.dll")]public static extern int SendMessage(int hWnd, int hMsg, int wParam, int lParam);' -Name a -Pas)::SendMessage(-1,0x0112,0xF170,2)
Or, you can use a Powershell script like this:
Add-Type -TypeDefinition '
using System;
using System.Runtime.InteropServices;
namespace Utilities {
public static class Display
{
[DllImport("user32.dll", CharSet = CharSet.Auto)]
private static extern IntPtr SendMessage(
IntPtr hWnd,
UInt32 Msg,
IntPtr wParam,
IntPtr lParam
);
public static void PowerOff ()
{
SendMessage(
(IntPtr)0xffff, // HWND_BROADCAST
0x0112, // WM_SYSCOMMAND
(IntPtr)0xf170, // SC_MONITORPOWER
(IntPtr)0x0002 // POWER_OFF
);
}
}
}
'
[Utilities.Display]::PowerOff()