How to Power off monitor from my c++ program in NT 4.0

Hi ,
I want to do Display monitor power off and on from my c++ program on NT 4.0
I tried doing with the sendmessage..
to the set the dispaly monitor in power off mode
SendMessage(HWND_BROADCAST, WM_SYSCOMMAND , SC_MONITORPOWER,2);
To activate the monitor again
SendMessage(HWND_BROADCAST, WM_SYSCOMMAND , SC_MONITORPOWER,-1);

This works fine on Windows 95 0r 98 but not on NT 4.0.
Can any one help me out.
Any help is greatly appreciated.

Thanks
Chakrad