Blank Screen

[cruella]

I have a Windows NT 4.0 workstation that the screen goes blank every now and again. If you hit ctrl, alt & del, you get the lock screen, logoff, Task Mgr, etc. box over the black screen. If I hit cancel, the screen comes back, but I don't know what is causing this. The screen saver is not set to lock and I don't know if there's a "sleep" mode in NT. Probably simple answer, any help?

[SMS Avenger]

we've found faulty power problems in the building cause this, also check the bios for a sleep mode.