Some months ago I bought a new ZOTAC Nvidia 9800GTX together with a new pc.
Everything went fine until yesterday, when suddenly while playing I got a black screen which immediately recovered, but after that my game was inredibly pixelated and the sound was stuttering. After a few seconds, the entire pc frozen and i had to reboot manually. Now, the same happens everytime, sometimes even as i browse the internet (so without any heavy stress).
I thought it my be the temp going too high, so I modified the fan speed; but nothing changed.
I upgraded to the latest drivers but with no avail. Sometimes, when the pc is on, I get a brief black screen and immediately after a recover, with a message saying: "Nvidia drivers stopped working and has recovered".
Some time ago I had the same problem (I think) with an old ATI card, and the "solution" was to downclock it. However I would like a better solution, since I don't think that things are supposed to go this way.
i had the same problem a while back, if you've got an older cpu (any single core) it may be that one of the chips are faulty try changing the cpu with another one even. if that does not work youve need to check your powersupply if your machine is not getting enough power it will cause underclocking.