Computer shuts down after some minutes

[plutomaniac]

CPU TJMax is at 100°C, so when Prime not reaches this temperature even with 100% at all cores, no game will reach TJMax.

Exactly, that's correct. Btw, it may be 105°C but that's not the point now.

I will first testing Furmark to stress test my GPU. And when my PC goes off, it's the PSU.

Alright. If you can, have some monitoring program open to see if the cpu stays under TJMax just to be sure about that as well.