Problem possibly with gtx 580 superclocked card

I'm hoping someone can help me. I built this system in Dec. 2010 and it has been working great until about 2 weeks ago. In the middle of playing a game, I would lose video. It would say "no dvi signal". The computer would keep running but no matter what I did, no video. I would reboot, and it would work for a while then the same problem. So, I opened the case and used compressed air to gently remove any dust/obstructions from the fan filters. I also checked to make sure the GPU was seated properly. Everything looked ok, except there was quite a bit of dust. The computer worked good for a week or so and now I can be playing a game and I get the BSOD and it reboots right away. One time the video froze and the computer just made a buzzing sound for a couple of seconds. It did not sound like a hard drive. I then rebooted and it was fine again for a short time. So I opened the case and removed and inspected the graphics card and installed it in a different slot, but I get the same results. Can anyone help me pinpoint what is going on? As I said, it has worked perfeclty for over a year and a half.

COOLER MASTER HAF X RC-942-KKN1
ASUS Rampage III Extreme LGA 1366 Intel X58
Intel® Core™ i7-970 Processor
Patriot Viper Xtreme 12GB (3 x 4GB) 240-Pin DDR3 SDRAM DDR3 1600
EVGA GeForce GTX 580 Superclocked
CORSAIR HX Series CMPSU-1000HX 1000W ATX12V
Logitech G510 Black USB Wired Gaming Keyboard


thanks,

Doug