computer shuts down

[Batwing]

A friend of mine has a strange problem. After running for a few hours her monitor will just shut off. It does not go to sleep. Moving the mouse and pressing a key does not wake it up. Her power settings are set to never shut off the hard drive ot the monitor.
I don't think anything is overheating because she can immediately reboot and the monitor is back on.
She has changed videocards and hard drives.
Here are the specs as far as I know them - motherboard: Asus, videocard: nVidia with 128 Meg RAM
Any advice would be appreciated.

 

[m3trj]

It might be a bad power supply. I had a very similar problem. Do you have another power supply that you can test in the system?

 

[Batwing]

The computer itself does not shut off. The power is still running. The monitor is the only thing not on. And I did try swapping monitors - same result.
I will try another power supply, though. Since the videocard does connect to the power supply, it could be the power.