Mate the only way is to start disconnecting things, have you got some spare parts to work with, if so, take the video card out and put another in, take one ram out then the other. Also did you change the bios setting to overclock. To get into the bios boot it and keep pressing the del, F2, F12 and F1 buttons one of them will get you into the bios. Set it to defaults. If I had to guess I'd say video card.