Faulty GPU or PSU?

Hi I am new here. My pc recently restarts playing some games which is strange to me. I did some internet research and found that it could be me psu or gpu.
My pc spec:
Intel core i7 870 (base clock)
Intel motherboard dh55pj
Sapphire hd 6870 igb
Transcend ram (4+2) gb
Samsung 500 gb hdd
Thermaltake smartpower 550 watt psu 80+ bronze

Also I borrowed a friends` 6850 gpu+ 450 watt psu to see if there is anu problem in my mobo or processor but it was just fine. But I gave my friend my gpu psu combo and he faced problems like mine after using them for 1 week.
So now I am certain that either my gpu or my psu has gone bad. but I cant know for sure which one.Any helps.....
 

cliffordcooley

Posts: 12,495   +5,868
Does your friend have a 500W PSU so they can test your GPU with their PSU? If they can test just the GPU, it might answer your question.

Actually 500W has head room, a 450W PSU might be enough to test for a week or so.
 

Skidmarksdeluxe

Posts: 8,645   +3,286
You say 'some games'. Try running 3d Mark or Heaven benchmark & monitor your GPU temps. Any temp in the 80-90 deg region is not good but some GPU's can handle it just fine. I'm leaning toward the PSU failing and that means a new one. If's you think it's the GPU, remove the HSF, clean the GPU, reattach the HSF after applying TIM (a decent brand). If you're lucky you may just get away with it.