Just got a green screen crash

Hi I was just playing L4D and all of a sudden the game froze I got a short sound loop and then the whole screen turned green for a few seconds. I then got a "no signal" message from my monitor. Is there something wrong with my graphics cards or could it be attributed to an unstable cpu overclock? I had no artifacts in game before the crash and it came completely unexpected. None of the gfx cards are overclocked at all only the cpu. I haven't monitored my temps in a while so maybe something is overheating? I have the GPU fan speeds set to 80% on both cards but ill try playing a game again and see if I get another crash.

What do you guys think could be the cause of this crash? I think I might have a slightly unstable CPU overclock because a few weeks ago I got 2 BSOD's but this is my first time ever getting a green screen and no signal crash.

My specs are in sig