I have heard these stories since the 8800's came out, many of them due to chip failure caused by overheating. If this is your case, then it's probably too late, but for anyone else listening, I'll pass on some advice I have heeded.

You will notice that the card's stock cooling fan is set to a low speed (~30%) to keep the noise down. Well if fan noise is not an issue, you can crank that up to 80-90-100%, keeping your GPU much cooler, and (theoretically) alive, a lot longer.

Aside from the noise issue, there is a probability that your GPU fan will die sooner when run at 100% (when compared to 30%). That said, my 8800gtx in nearly three years old, the fan sounds like a vacuum cleaner encased in a foam box, but it still works...