If the screen contains a lot of black or dark space, the monitor blanks out.
if website contains lots of black, the screen goes blank when I view it. Or if I use Microsoft photo editor, and I turn the pictures brightness down a bunch, it causes my screen to go blank. I can press (Alt Tab) to switch to a different program, and things are fine.
EDIT: I recently upgraded my computer to a Athlon 64 processor, e-GeForce 7950 GT KO graphics card, and ASUS M2NPV-VM motherboard.
Have you tried forcibly disabling the onboard video? Due to the onboard and the add-in card both being GeForce chipsets, it could be that the board is failing over to the onboard GeForce 6150 instead of using the add-in GeForce 7950GT.
Another thought: how old is your video card? I notice it's an eVGA GeForce 7950GT KO... given that those cards are factory OC'ed, perhaps you need to try down-clocking the card to see if it's the card starting to fail due to OC.
This is almost certainly a hardware problem. The question is whether it is the video card or the monitor that is causing it.
When you say "blanks out" do you mean that it goes into standby mode, or just that the entire screen becomes black but the monitor stays on?
Is it a CRT monitor or LCD? Have you tried the monitor on a different machine, or a different monitor on the problem machine?
I have seen televisions shut down when they get too bright, due to electrical problems, so it's not inconceivable that your monitor may have some problem which causes the same thing for a different reason.
Try swapping monitors and computers, so that you can at least isolate the problem.
Edit: Here is a description of a similar problem relating to CRT televisions.