PC starts lagging and black screen

[Tr0jTo]

Hi guys. I am having a problem where my pc after a while and i am not sure what causes the problem sometimes it happens when i start playing games but even when i watch videos on youtube. The pc starts to lag , than it freezes and screen goes black and when i am playing a game the sound freezes too and stops. The computer is still running , no shutdown or restart until i do it manually, With no errors or warnings. I dont know if its an hardware issue( probably HDD) or software (virus , bu thats unlikely i scanned the shit out of it)

 

I am running Windows 8.1 64bit

 

CPU: AMD Phenom II 1100t X6

GPU: nVidia GTX 560

Cooling: 2x Noctua NF-p12 120mm fans

              Corsair H80i (closed water cooling)

HDD: 1x 250 Gb

         1x 1000 Gb

Motherboard: ASRock m3n78D

PSU: Cooler master 620W 

Ram: Kingston 8 Gigs DDr3 (4x2)

 

Any advice will be helpfull , thanks in advance.

[Extingquish]

Is the graphics card overheating? 

[Tr0jTo]

100% not

[Tr0jTo]

My SATA cable from the hdd was cut .... i dont know how that happen and by cut i mean the insides were exposed and it probably touche the frame of the case a few times so it froze .. i dont know ... for now its fixed