Computer restarts every time I try to play a game

Hey guys,
Lately I've runned into a problem with my desktop. Almost everytime I launch a game the computer just restarts, no BSOD or anything (option for that unchecked), just restarts.
Already did a clean install. removed all ram slots one by one, assembly the computer from scratch, blow the PSU.

Did a benchmark to CPU and GPU both went fine

Setup:
R9 280X,
AMD FX6300,
12GB RAM DDR3 1600Mhz,
WaterCooling Corsair Hydro H55,
PSU Corsair 550W

Running Windows 8.1

The PSU is still on warranty time but I will be without a computer for that time, I dont know if I should buy another PSU or just put this one on RMA and wait because I'm not sure this problem is from PSU (hardware aint my strongest suit)

Thanks

Computer restarts every time I try to play a game