PC ragequits while running CPU/GPU intensive problems

Could you measure the temps of your CPU/GPU while the error occurs? Also If you are using the standard Intel HSF please ensure it is seated properly as that is often the main cause of problems.

Last time I checked they where around 40c.
Problems started occurring about 2 days after I installed the cm hyper212evo with a second fan.

Try to test with another RAM to see if you have the same problem,or give the ram an ram test and to cpu a cpu stress test and after that if there is no problem try to the gpu a test to,to see what is happening.Good luck.

The problem appears to be completely random now, I mean it occurs at random moments.
Doesn't matter what I'm running.
I think it always was random, but I was running things like games after an hour of PC usage, problem occurred after an hour of PC usage most of the time.
Also, one thing I noticed, for every time it crashes, it will crash faster the next time.

Other than that, I used Prime95 and memtest and they all came through fine.

Usually when you see artifacts like that it means your video card is overheating thus leading to crashing. Like you said, it crashes quicker after the first crash, and that's because the hardware hasn't had sufficient time to cool down between crashes so it's reaching those dangerous temps quicker than from a cold start-up.

Have you overclocked any hardware?

I'd dust everything out completely as dust insulates hardware making it run hotter.

Make sure all fans are spinning and that they're spinning in the right direction for optimal cooling. Front/side fans should be intake and rear/top fans should exhaust. If your PSU is a bottom-mount and can be flipped to where it's intake fan is facing the bottom of the case (as long as there's a vent there) it'll help with GPU cooling.

And performing a wire-tuck in your case if you haven't already; it'll improve case airflow.

Awkward, I don't see any excessively high temperatures.
http://gyazo.com/c9e149c17d6dee29fc58a8fb91cddee6
My graphics card isn't overclocked btw and I have the same problems while running from the CPU's integrated stuff.

Hmm, were you able to test the temps just before the crashing? I'm almost certain it's an overheating issue since it crashes quicker after the first time. Try running a different temperature program for your processor. And after it crashes next time try and feel the processor heatsink with your fingertip. It should be pretty warm but not HOT to the touch.