From what you say I understand you think it's a software issue. So go back to factory conditions and see if it still crashes. Choose a game that doesn't need steam to experiment.
If you can reproduce it, and bought this a gaming PC, it seems a warranty case.
Kees
Alright, ever since I downloaded Black Ops 2 on steam my PC just starts crashing and rebooting. I thought that it was just because of the game and I started playing other games and they started crashing as well. I am very frustrated and I have looked it up and everyone has different answers. Could someone help please? It is a new build mind you. Here are my specs:
Intel Core I7 4790k (stock fan)
EVGA NEX 650G (power supply)
GTX 980
Fatal1ty 797 Killer (motherboard)
32 gb of RAM
Went into the event viewer and all it said was "The system has rebooted without cleanly shutting down first. This error could be caused if the system stopped responding, crashed, or lost power unexpectedly."
Also my temperatures are normal so I don't think that is a problem (peaking at about 50 C)
Tell me if you need any more information.

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