Black screen problems when playing games. Originally thought it was the PSU but we changed it

[abcandyabc]

So, after i got a new pc, i gave my old one to my friend. i bought a new drive and some new case fans and gave it to him and set it up. Everything worked fine for the first week of two as it did for me when i had it.

After a while he started to get some problems when he was playing games. He played PLAYERUNKNOWN'S BATTLEGROUNDS and Overwatch mostly, and he started to get crashes randomly within games. He could sometime play 3 or 4 games, and then crash on the fifth one. sometimes it would be on the first game or even when he loaded the game up.

 

The types of crashes he would get would be a black screen and the PC would reboot. The LEDs on the case and fans would still be on but the PC would load up windows again as if he just started his PC. 

My first thought was, check temps, and replace PSU. The temps were fine as they were when i used the PC, and i used my current PSU, which is fine, to see if it was a power problem. At first it was better and we played 6 or 7 games with no problems, when it suddenly decided to crash. I ran cinebench, 3dmark and heaven valley and it ran fine, no crashes, and everything was as it should be. It WAS literally only when playing games, until today when i got told that he crashed while browsing the steam store. 

 

PC specs:

CPU: AMD FX-4170 quad core

Motherboard: Gigabyte GA-78LMT-USB3

GPU: GTX 660ti

Ram: 8GB (not too sure brand)

PSU: Corsair VS550 550W

 

I am out of ideas on what it could be, and my next step was to reinstall windows. I used to have the issue with the PC too, and changing the PSU was the fix for me... problem is he has the PSU that i changed to, and now it doesn't work.

Reinstalling windows is the last thing i can think to do, or get another PSU, and then send it back if it doesn't solve it. Ive attached his DxDiag if needed, just in case there's something i missed.

Any help would be great because ive had a look online and no solution has worked for me yet.

DxDiag.txt

[luigi90210]

I don't think this is the right section to ask this but it could be poor power delivery to the power supply. Have you tried hooking it up to a UPS?

 

The only thing I can think of that would cause this on a known good power supply is that the computer is using more wattage than the PSU can supply or there is faulty wiring in your friends house and the PSU isn't getting a good stream of power.