Bitttymacod
To Bennassi -- Desktop AMD Athalon 64 3200 2.01 GHz/ 2GM memory and Nvida 9600 GT. The power settings are set to "leave the bloody computer alone, I'll turn it off when I go to bed."
I had very similar issues on nvidia 9500GT. Did every thing you can imagine with no help.
Then i solved it: open your PC case, find the nvidia piece and clean it from the dust. Works like a charm after doing that for me :) The problem was simply the clogged gpu fan, and the overheating gpu as a result.