I'd like to start off by saying I don't know very much about computers so please if you choose to help explain like I am a child. Two days after buying Overwatch my PC rebooted in the main menu when I launched the game, after messing around with fan speeds and updating drivers the problem was still there, then after an hour I tried to launch again and the problem seemed to have disappeared, so then another two days go buy and my PC reboots in the middle of a game I try to launch Overwatch and it reboots in the main menu again, I try it the next day and I manage to get one minute into a game and it reboots, now it's back to rebooting straight away. I doubt overheating is the problem, temp goes up to 75°C at it's highest.
Specs:
OS: Windows 10
CPU: Intel Core i7 950 @ 3.07GHz
RAM: 12.0GB Triple-Channel DDR3 @ 530MHz
Motherboard: EVGA X58 SLI Classified
Graphics Card: 3072MB ATI AMD Radeon R9 200 Series
PSU: Corsair VS650