at least three or four of the times that my powerbook has been declared dead the expert making the declaration was an Apple Genius and the Apple store. each time they would declare it dead, then offer to sell me a nice new computer.
i would decline and then buy a new battery or a new power supply or whatever i thought was the problem. and when i would get it home it would work again. the apple geniuses did not believe in my powerbook, but i did.