I agree with gull04 that since you've re-seated most things and you still have the same problem then it could be something stupid.
From your post, this worries me:
Quote:
DEC 01 18:59:31 : 0004000e: "SC Request to Power Off Host Immediately."
So where is that coming from? Perhaps some button stuck in on the front panel? Key switch stuck? Or something like that is where I'd be looking.