3d Apps Crash

[Offsite]

When I start a 3d application, or firefox 4 beta 12, my computer crashes. Either the monitor stops receiving a video signal, or video cuts to a solid color and then in a few minutes the monitor stops receiving a signal. That is the current state, but has not always been the case. I have RMA'd the video card twice now, and my power supply has died. The first thing to happen was the dead power supply. I simply RMA'd the power supply and went on with life. Later the video trouble started. It started with the crash to solid colors depending on the last frame rendered, the audio would continue as if nothing happened. It seemed obvious it was a dying video card. I found I could stop the problem by underclocking the card. I used it like this for a while, until I could find time to RMA the card. Upon receiving the second card from EVGA, the problems returned, only this time underclocking the card did nothing. Instead of solid colors, the video would crash leaving the last frame rendered on screen with a speckling of colored pixels over top the the frame, this being consistent with video ram problems. So I RMA'd this card. EVGA graciously sent me a GTX 285 to replace my GTX 280 that I had paid for on this second RMA. The new card worked well for 2 or 3 months, but now I am stuck back where I started (with the description at the beginning). I have run memtest x86 for 10+ hours straight, prime95 for approx. 6 hours. I have also tried updating all the drivers on my machine, as well as updating my motherboard bios. I have tried running each ram stick individually, and my operating system gets re installed a minimum of once every three months so it has to be hardware or configuration related. I am reaching the end of my patience and I really need someone's help how have some new ideas. At this point I think it is my motherboard...
Also, I have rigorously tested the voltages on the 12 volt rail at idle as well as under load, and under crash conditions. Any help anyone can give would be much appreciated.

My Machine:
cpu i7 290 @ stock speed
mobo asus p6t deluxe
ram 6Gb corsair @1333
psu Corair TX750W
wifi asus pce-n13
os windows 7 x64
antec 1200

ps I have watched temps with various programs, nothing abnormal

 

[rolli59]

If your motherboard was broken, would it run fine for 2-3months? The only way would be if it was supplying the card the wrong voltage through the PCIe slot and eventually killing the card.