My PC Keeps on Shutting Down

Not every 5 minutes, but just when it wants to. I was watching Gmod Idiot Box on YouTube While playing GMoD, having a good time, then my PC shuts down without me telling. I power it back up and it seems normal. No, it's not because it wants a Windows 10 update. I delete those.

Specs:
http://pcpartpicker.com/user/doaler4sback/saved/BvhhP6