I've had a similar problem with my color classic: I removed the logic board and blew out the dust with canned air and when I put everything back together the color classic wouldn't boot.

After trying pretty much everything (new pram battery, new HD, various boot disks) I finally tried using a 25 pin SCSI active terminator.

After I installed the SCSI terminator and fired it back up, it booted into System 7 without a hitch!

I don't know why all of a sudden I now need to terminate my CC, but I am certain that it solved my problem.

The part was $12 on Amazon.