New PC is powering off. Is it overheating?

Hello,

I finished my first build on Friday. Today (Tuesday) it started powering off at random. I was just browsing and installing Skyrim mods (Skyrim was not running) so it seems an unlikely time to overheat, but I don't know what else would cause these abrupt shutdowns. Is there a program you guys would recommend to monitor temperatures? Is there another cause I should be investigating?

 

Windows 8.1

i5 4690k

Cooler Master Hyper 212 EVO 82.9 CFM Sleeve Bearing CPU Cooler

Gigabyte G1 GTX 970

did you apply thermalpaste?

and how did you apply it?