Computer crashes when playing games

First of all, I'm sorry if I post this in the wrong section, please move it if so.

So, as the title states, my computer is crashing when I run games and possibly other programs that demands a lot from my computer. I'll start with some back story.

First of all, I recently got my computer back from repair after a long time. They replaced the graphics card and the motherboard, and possibly other parts as I haven't really checked it out yet. I returned it to the manifacturer, so it should have been working now. Everything works fine, it was on all night to update software and drivers, download games and so on with no crashes, and the problems didn't start before this very morning.

The first game I ran was Far Cry 3, a very demanding game for my computer. The specs are good enough to run it, even with almost highest possible settings on everything. I didn't get longer than the first time you meet Vaz, where he talks to you while you're in the cage before it crashed for the first time. What happens is that the computer just freezes by sometimes getting a black screen, sometimes a black screen with weird lines and sometimes just a not responding monitor. First I thought it was Far Cry that was the problem, as it demands a lot from your computer, but then I tried other games like CS:S and Garry's Mod with the same crash happening.

Then I ran a CPU stress test putting both CPU usage and virtualy memory to 90-100%, and it still didn't crash.

SPECS:
Graphics Card: AMD Radeon HD 7800 Series
Processor: Intel(R) Core(TM) i7-3770 CPU @ 3.40GHz (8 CPUs), ~3.4GHz
Motherboard: ASUS P8Z77-V LE PLUS
RAM: Kingston DDR3 HyperX 1600MHz 6GB Kit
Operating System: Windows 7 Home Premium
PSU: Chieftec Nitro Series BPS-650C 650W PSU
SSD: Corsair SSD Force Series 3, 60GB, SATA 6 Gb/s
Hard Drive: Seagate Barracuda® 7200.12 1TB SATA 6Gb/s

Thanks in advance,
Kimaz
 
Turn off or disable CPU thermal monitor and C3/C6 state support. You will find these under Advanced Frequency Settings/Advanced CPU Core Features in the bios. This should help the game play
 
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