PC problems

About five days ago i booted my PC up and i got a horrible looking green screen so i reset the PC but then it would no longer start up, just power on then turn back off.
So i messed around with various things and nothing worked until i booted with only one RAM stick, i then put the other ones back in one by one and it still worked fine for five days. Now this exact thing has just happened again, and again i did the ram stick thing until the PC booted again (Left one out as when it was in PC did not seem to boot) however when i plugged the monitor back in there was signal just no picture and occasionally it would flicker white or green(Same green texture as before), so i changed the cable connecting it to the PC and it displayed a picture again, i then tested the cable i just took out and it was working to.

Really don't know what is causing this as everything is working fine again now, if anyone has any suggestions as to what the problem might be?

Card is GTX570