pc shuts down w/o warning, need help please

[SkizmX]

Ok, so I recently built my first pc about 4 months ago. My pc had been running pristine till about a month ago, when it started shutting down without warning. I have added 2 120mms fans, for a total of 4 fans (1 came with the case, the other with the cup). I have also cleaned off the old thermal paste and added new Attic Silver 5 thermal paste. The Specs. Are as follows:
MSI 970 gaming mother board
AMD 6300 black edition processor
2 TB HHD
AMD 270 Crimson graphics card
650w psi
Any help would be appreciated, as you can see I have pretty much done anything to prevent overheating issues, except adding a liquid cooler.
ATM all that I am really playing is League of legends, and watching YouTube or doing school work on my pc.

 

[gussrtk]

what temps is your CPU/GPU running? (possible damage preventive shut down)

What is the PSU brand? (possible PSU failing when under load)

Have you run memtest?

last option possibly to check memory dump for a failed system in OS. I think it's called "whocrashed" but look at the upper options first