is clean inside? I have some experience with a 1 dead powerbook and 1 dead macbook pro, both with similar symptom and both pretty dirty inside...dirt stuck inside the fan's and vents...the overheat kill the graphic card. Some post on youtube recommend to bake or use a heating gun. I replace the mother board and both are working again. (before the surgery I didn't get any kind of
response when I push the power button).