My computer seems to be frying video cards...

Hey there, I have a computer which I had assembled at a specialty store about a year and a half ago. Up untill maybe a month ago it had no problems, but I first started having issues when, when I went to boot the computer, it would freeze right after bios while loading the operating system. After a few reboots and system recovery's, I would be able to get the computer running, and the only way to make sure that it would load up after a cold/hard boot would be to reinstall the graphics drivers. For whatever reason, this would solve the problem untill maybe a few weeks after the same problem would happen again, and be remedied by the same solution. Then I started noticing freezing issues in which, while playing a game (it happened in Halo 2, Battlefield 2, World of Warcraft, the game would just freeze the screen and the last sound would sit there stuttering untill I rebooted the computer. It eventually got to the point, that Whenever I would try to update drivers, whether they be from a cd or a new release, it would freeze the computer about halfway into the install process. This card in question was the EVGA 9800GX2. I told this to EVGA and they said to send it in, and when I got a replacement today it was a brand new card, meaning that the card I sent in was most likely toast.

In the meantime while I sent in the 9800GX2, I picked up a EVGA GTX260, and it worked fine for about a day or two untill it began freezeing, the exact same way the 9800GX2 would, where it would freeze the screen, and stutter the last sounds. These types of freezing would happen intermittently across multiple games, untill after about 5 or 6 of these types of freezes, when I went to play battlefield 2, the screen artifacted (sort of went all garbled and pinkish with almost a checkerboard effect) after only a few seconds into the game. When I reset and went to turn it on again, the computer began to POST, but wouldnt finish. My motherboard, the EVGA nForce 780i would show a post code of 26 on its card, but what was weird is that with no video card it would post to FF and then obviously stop because there is no GPU, and with an older household PCI video card, it would post normally and boot the OS.

I took the GTX260 into the store I bought it from, and after they tested it they said it was indeed a problem with the video card where it wouldnt post, and gave me a free replacement under their exchange policy.

So my assumption is that something in my computer is frying the video cards that are at least in PCI-E slots. While I was troubleshooting my first video card, I tried it in the different PCI-E slots, and they all seem to be working. Im now thinking that it is either the mother board or more likely the power supply. I have the OCZ gameXtreme 1010w power supply, and the video card is the aforementioned evga nforce 780i. I have also gotten the impression that for some random reason this could be a hard drive issue, so my hard drive is the Seagate 500gb 7200.11 32MB ST3500320AS . It's a touchy subject because I'm scared to put in either of the replacement video cards I have now because I dont want them to get fried. Any suggestions?