Why would this happen?

I took my computer to my buddy's house to troubleshoot my video card, which I haven't been able to run 3d apps with since I bought it, since his platform is comparable to mine. I have an Evga 6800GT and he has a BFG 6800 GT OC. So we swap cards, make sure the video drivers and settings match from one box to another, and he proceeds to play bf2 with no trouble. With his card in my box, I can't even boot windows. So conluding that my card is fiine and that my problem stems from incompatability with myy NF3-250 chipset, we switch cards back. Now my buddy's system won't boot with his own card. We are like, wtf? We swap cards again with my card in his box, and it still doesn't boot. We swap back and my card boots fine in my box, his box is dead.

This is a first for both of us. We are stumped. There's no way we fried anything, yet his motherboard and video card no longer work.

Help me Obi-won-Knobi.

....an update.

I put the card into an older A7N8X Deluxe and I got the red light of doom(video card dead).

I had a very similar problem to the you originally described. As far as I could tell, it was because my board did not support AGP 2.0 (even though it was supposed to). I had like 4 video cards to test with, two AGP 1.0 or whatever, and two 2.0s. With one of the 2.0s I could run Windows for the most part, but 3D was an instant reboot. The other couldn't even get into Windows. This was an EPoX board and an older generation though. I do, however, have a NF3-250 now (Chaintech) and I have a 6600 GT. I assume that means a 6800 GT would work as well. :p:

Anyways, how do you know the motherboard doesn't work? It sounds like there might be some really dirty pins on his video card or in the motherboard slot. Might want to try swabbing them clean. But if you're just guessing the motherboard doesn't work, please specify. It sounds like you guys have some idea what you're doing, but you weren't too specific on the troubles you're having. Are lights blinking, fans spinning, etc.? There could easily be a power supply issue here, who knows.

maybe your shit fried his?