well recently my graphics crd crashed my pc, by producing artifacts and weird colors on my screen, stock speed. So reinstalled drivers worke3d fine then nice blue screen on diagnostics. Every time I boot up, some words/letters on post screen are purple of white. Looks cool but not a good sign I think. So I was doing a memtest86 and at 47 percent PC just looses power, recently new 550W PSU, been working fine for a while and NO problems when installed or whatsoever.
I'm pretty sure its the graphics, My ram is not overclocked, everything at stock.
p35-ds4 Gigabyte Mobo,
Q6600 Core 2 Quad
4GB Kingston DDR2 667 RAM
Gigabyte 8500GT 512Mb graphics
Coolermaster 550W PSU
6 system fans,
plenty of ventillation.
graphics has no fan, heatsink only.
rest nicely air cooled,
Your gpu may be faulty. NVidia's Geforce 8 series low end and midrange cards were plagued by faulty chips during their production; specifically, they literally cracked under heat. Since you have a passive cooled solution, and passive cooled gpu's tend to get very hot, this may be the case for you. The only way to know for sure would be to try it on another comp and/or boot in vga mode (hitting f8 while you boot and selecting the "vga mode" option). If the problems persist during vga mode, you have faulty hardware (might not necessarily be the gpu, though). If problems occur on the other comp (if you have one to test with) you have a faulty gpu. If all goes well during vga mode, but problems still persist during normal startup, you have a driver conflict. Post back your results.
P.S. your gpu may be under warranty for replacement depending on who your manufacturer is and when you bought it.