Distorted graphics whilst playing a game

distorted graphics whilst playing any game but the picture seems fine on the start up screen phoned ms support to be told it will cost me £94to fix but as the console is a refurbished unit they sent me in october as my original got the RROD i think that is total s*** they should fix for free but wont even entertain the idea, i am thinking of opening my console up and havin a fiddle with the wires and connections as i cant play it anyway any 1 got any other ideas