Serious video distortion using an XFX 7900

Hi,

I have an GeForce 7900GT made by XFX and I find that my system is sort of crashing when I push the card too hard. The computer itself is overclocked, but I've confirmed that this problem happens when running all the components at normal speed. Also, since XFX has a good warranty program, I've had this card replaced, so I'm pretty sure it's ok.

Under normal circumstances the card runs just fine. I can play Doom 3 without any problems, and the system remains stable even with the detail, AA and AF levels set high enough that the gameplay is really choppy. However, when I play games like Dawn of War, or Star Wars battlefront 2 under anything other than the absolute minimal settings the whole game will freeze. After about 30 seconds the game will resume, but with significant graphical artifacts (smeers, extruded surfaces, etc). The games will do this until they finally crash and I get the windows cursor back. After a crash the system is pretty unusable. The applications still run ok, but I never get the whole desktop back, and the crashed game is laid over the normal desktop.

I've tried installing a clean copy of windows on a spare hard drive, but ran into the same problems. I've also tried to stress test using prime95, distributed.net's client and 3D Mark. None of them have crashed the system.

I'm using an XFX 7900GT (pci express), a gigabyte GA-G1975X motherboard, and the nvidia drivers 93.71, and right now I'm at a loss. Any suggestions would be greatly appreciated. Thanks!