Garbled display on Inspiron 9100.

I have had Inspiron 9100 for almost 2 years now and just recently I have started having garbled display whenever I try to play games. I have ATI mobility radeon 9700 and I have tried a lot of things. I formatted my hard drive, reinstalled windows, updated my bios, got the latest video drivers, opened up and cleaned my laptop, consulted with the guys at Compusa. I tried connecting a monitor to my computer I experience the same problem with a different monitor as well, so I don't think it's my inverter board that's broken. If it is a hardware problem, it could be a malfunctioning video card, but it is somewhat expensive to replace. Can anyone give me some advice as to what i might do?

Thanks!