[System.Runtime.InteropServices.DllImport("user32.dll")]
public static extern IntPtr SendMessage(IntPtr hWnd, uint msg, uint wParam, int IParam);

class Program
{
private const uint WM_SYSCOMMAND = 0x112;                    //系统消息
    private const int SC_MONITORPOWER = 0xF170;                  //关闭显示器的系统命令
    private const int MonitorPowerOff = 2;                       //2为PowerOff, 1为省电状态，-1为开机
    private static readonly IntPtr HWND_BROADCAST = new IntPtr(0xffff);//广播消息，所有顶级窗体都会接收

　　[System.Runtime.InteropServices.DllImport("user32.dll")]

    private static extern IntPtr SendMessage(IntPtr hWnd, uint Msg, int wParam, int lParam);

static void Main(string[] args)
    {
       SendMessage(HWND_BROADCAST, WM_SYSCOMMAND, SC_MONITORPOWER, MonitorPowerOff);
    }
}