I bought a refurbished 60 Gig PS3 during the summer from Gamestop. At first the system worked fine. Now whenever I try to load a new game (ps3) it promptly freezes, or has graphical issues. Grand Theft Auto IV, Call of Duty 4 (first games I bought) and ps2 games all work fine. But Guitar Hero World Tour, Mercenaries 2, and Motorstorm refuse to work properly. I've tried two sets of cables. Two different HD TV's, and also I've reformatted and re updated my ps3 twice. Any ideas, I've also used a disc cleaner.