it can be from graphics card , drivers,heat...etc OR Ram(take them out from the slots and clean the golden pins with some white clean paper ) . After doing that come back and tell me if it worked!
Just looked at youer case and its the same as mine but I bought mine unbranded. As stated it could be an overheating issue run HWMonitor to check you temps while gaming just try to get out before the crash so you can see what they reached. What fans do you have?
Yea temps look fine(pls monitor the m/b temps too). As rd2cyp mentioned check for the psu output using a psu tester, not too sure if that will give u accurate results without any load on the components. If it wasn't giving enough output the pc wouldn't boot, but it's rebooting only with load. If you have /can borrow a spare 600w psu can save u those 10 bucks. If not that's a start