Hey, so I've faced this problem, and I am not completely sure what is causing it. When I use my PC for long periods of time (+12 hours non stop) my PC sometimes simply freeze and I have to restart it in order to fix it. For example I will be playing a game, like CS:GO, and it will randomly freeze on one frame. If I'm listening to any sort of music at the time it freezes as well which leads me to believe that the system simply refuses to work if I do not restart it after the freeze.
First I thought that it has to do with CPU overheating as PC case's window seems to be quite warm around the area of the cpu when ever crash happens, but the temperature displayed in various apps seems to be normal.

Things I've tried doing:

• Making my cpu cooler fan operate faster through BIOS
• Switching RAM sticks to different slots

I don't think it's relevant, but here are some parts of my PC in case its important:
CPU: Intel(R) Core(TM) i5-6600K CPU @ 3.50GHz
CPU fan: Cooler Master Hyper 212 EVO
GPU: GTX 970 Gaming 4G

By the way my case fans are working around 2 times slower than my CPU fan if that might be causing the problem.
Anyways post any suggestions or guesses, everything is appreciated, thanks in advance.