Hey, I have exactly the same issue here. First I think I wittnessed it becoming worse about 2 years ago. Then had it running for months without rebooting. I tried different harddrive, ram, disc-drive and battery, but it stays the same. In my case the screen flashes once for about a millisecond when I try to turn it on. My MacBook also won't wake up from suspend, so I really have it to stay turned on. Did you get on with yours?
