SO HELP!

Recently well lets say 1year ago my 8600gts Stoped Working on my computer for some reason. I have a Custom Built Computer so i will put specs Below.

About 2 years ago i bought a Evga GeForce 8600GTS so i can play crysis on my computer and i Pluged it in my computer PCI-E Slot , and i saw that it has a 6pin power connector . Everything Worked Fine!!. Untill 1day i decided to uninstall my antivirus to get a new one and it just turned off. STOPED WORKING!! so i put in my old GPU Nvidia GeForce 7300 Gs and it works.
So i said " W T FFFF ", and thats the end of me using that 8600GTS. It was on my dad's computer and so about 3 or 4 months ago i bought my own computer parts and builted my own computer ,i used the 7300gs that worked and my dad bought his own GeForce GT 220 Low Profile . I didn't say anything and i did try that 8600GTS again and i did not have high hopes.

So about a month or 2 ago i bought a PNY GeForce 9400GT From a Friend and i tested it and it works fine. but i am not satisfied. Because that 9400gt is even though a Higher Series It only contains 12.8 Gb/Sec Memory Bandwidth. :*( , While the 8600 GTS had 32Gb/Sec . So i Told my friend to see if he can try to fix my GPU, he said "Sure, I'll Test it", Next day he brought it back and said " It works just fine , except it was too hot so i cleaned it and now its fine " . Those were his exact words. So now i am PISSED OFF. Any help with getting that 8600GTS to work?


My Computer Specs:

MotherBoard: MSI 785Gm P45
CPU: Amd Phenom(TM) II X2 560 Processor (2 CPUS), ~ 3.3 GHZ
Memory Ram: Agama Gaming Series 4GB Ram
Graphic Card : PNY GeForce 9400 GT ( my system says i have 2gb of mem but i actually have 512mb XD)
PSU: 430w