Computers shuts off while trying to play games

[jjrocks24]

Hello, i just recently built my computer and for some reason sometimes it just randomly shuts off during games... sometimes in amnesia, and sometimes in Slender Arrival Beta
PC Specs
i5 3570k 3.4 ghz stock cooler for now ( temps havent gone over 45*C)
EVGA GTX660
Kentec 1000w PSU
8G of corsair vengance RAM
5 Fans 3 blowing in 2 out
Mobo Gigabyte Z77 UD3h
1TB Western Digital Caviar Blue

This computer is 2 days old.. cant find the problem thats wrong... someone help

 

[XYMan]

Defected PSU unit.

 

[faster23rd]

Most likely, given the model's unknown manufacturer.