One final thing to try is turn the machine off, open it up, and pull the battery out of the motherboard. Wait a decent amount of time (five minutes or more), reinsert the battery, and restart. This should force your machine to forget about anything it thinks it knows, and go back to the factory configuration. Your CD drive should now boot the machine (when holding down 'C' during boot). I've seen reports of this working for more than one person, but there have been a couple poor souls that have tried this and are still non-functional.
Any other thoughts on potential solutions for those still stuck?

