Problem Solved!

It turns out it was the ribbon cable for the combo drive that was causing the problem. I unplugged it and it booted up just fine.

That makes getting replacement parts a much, much cheaper proposition, since all that it needs now are new screws (I lost most of them), a sleep LED board (one of the wires broke; I may try fixing it first), and of course the combo drive cable.

Until next time...

c