I recently upgraded my gpu from a 9800gx2 to a gtx 580, and since then, my computer has been crashing to a black screen a few minutes after starting a game, or a bit longer when watching videos. I had the same problem with a hd6970 I bought, but returned for a refund because I thought the card was bad. My 9800 still works fine, and I'm pretty sure neither my CPU nor gpu is overheating (this has happened with an open case). My power supply, an ultra x3 1000w that's about 2.5-3 years old was in operation when my motherboard fried a few months ago. I don't own a multimeter, but according to my bios, the rail outputs are within normal ranges, except that my 12v rail is outputting at about 12.6v (this is in the bios, so I'm guessing that's idle?). Under clocking the card seems to delay the problem quite a bit, to the point where I can play games for much longer before the crash occurs. The crash dumps point to a file called nvlddmkm.sys, which, after researching online, can be caused by many things. So, do you think the issue is with my psu, or something else?