Thanks for the reply, but these machines don't have a "left IO board" I believe that's only on the macbook pro's. On this unit, it's all built in to the logic board. rab777hp, when you refer to the power supply, do you mean the AC adapter, because there's no seperate power supply board or anything. If so, the AC adapter is definitely working, and besides, the battery has a charge, so even if it wasn't the laptop should start up on battery. I'm also wondering if anyone knows if the PRAM battery could cause this situation???