Well I tried a different monitor on this PC and the same thing happened. Is there any way though that I can test the mobo? It probably is that, as not long ago the PC went in sleep mode, but then the power went off also. I checked the wiring of the power supply, as i may have done something wrong so we'll see if it happens again.
Also, forgot mentioning before, when going in sleep mode it says 'no video input'. Unsure what it said when the PC went in sleep mode without playing a game before, but i'll see if i can find out what it says then.