PC keep powering off after 5mins?

Just put together a PC to use as a linux box (has Xp on there at the moment), but it keep powering off after 5mins?

All the temps are fine, voltages reading off the sensors are fine, and even checked the PSU with a multi meter and they are all good.

have quadruple checked all the connections, and done some random acts like switch the GPU to the second pci slot, and different ram combinations from 2 to 8GB.

Any thoughts?

Perhaps it is something to do with a circuit breaker in the house (stupid suggestion, I know but Its worth a try)

I had random outages and my Pc would just go dead and then be fine, i checked everything for about 4 hours, though it might be my PSU going bad and the Built in protections kicking in ect... 

Turns out it was a broken plug and when my cat or foot would bump the cord it would ground out, still have to replace said plug but theres always that possibility its not the PC itself.