//关
SendMessage(Application.Handle, WM_SYSCOMMAND, SC_MONITORPOWER, 0);
//开
SendMessage(Application.Handle, WM_SYSCOMMAND, SC_MONITORPOWER, -1);
SendMessage(Application.Handle, WM_SYSCOMMAND, SC_MONITORPOWER, 0);
//开
SendMessage(Application.Handle, WM_SYSCOMMAND, SC_MONITORPOWER, -1);
it cann't work under win2000