I have a new to me 15in 1.67 ghz powerbook. I just put a fresh install of 10.5.8 on and all was well until it started randomly going black and putting itself to sleep. It does this whether plugged in or not and requires hitting the power button briefly to light the screen back up but it usually blacks out again in a few secs. It doesnt seem very hot, which was my first thought. Also the battery was holding a decent charge prior to these black outs. Any ideas of what it is would be greatly appreciated.