I finally scrounged up enough parts (i think) to upgrade my trusty 840av to an 8500 power mac. I have the 8500 logic board, a 150 mhz processer board, and the 8500 rear panel. I thought this would be all that was required, maybe I'm wrong.
The 8500 logic board is used, and came with 32 megs memory, and a cache chip, but that's all. After putting all the pieces and parts together, I tried to boot the computer, but I get no start up chime, and the monitor stays dark. The hard drive spins up, and the power on LED lights up, but nothing else. Am I missing something??
The 8500 MB did not come with a ROM chip (which I think I need, right?), so I took one out of a 6xxx something MB that I had laying around. It plugged in, but is too large. I also changed the battery with a fresh one, but it didnt make any difference. Can anyone lead me in the right direction with this upgrade, as I don't know what to try next.

Thank you in advance...Brian