Aurora R4 Crash and Reboot While Gaming

 I got my Aurora r4 from dell in december .. bought myself a christmas gift .. First month was awesome , no problem with anything , Expect some ( lots) of flickering in CoD ghost , but not in any other game ... so that was  Kinda fine with me .. but it has been to week , while im playing , The compturer shuts off and reboot on it own , Everything seems to work fine after that , ive ran Dell diagnostic and Pc checkup , everything was fine and no problem detected ...  anyone had an experience like mine and know the solution , Cause im getting frustated

Pc spec  :

Intel Core i7- 4930k 3.4ghz

Bios Version : A10

Graphic Card : Radeon HD 8990 ( latest Driver installed )

Windows 7 Ultimate Edition ( up to date)

32gb Ram