The best way to diagnose your cdrom failure is to physically uninstall it and then reinstall it. Just shut her down, pull the ide and ribbon out of the cdrom and reboot. Check your hardware profile as you may have to remove the cdrom from it. Then shut her down again and plug the ribbon back in. Boot her up and see if your system recognizes and reinstalls the cdrom. If it does, test it out and see if it reads.
I've had cdroms just stop working, but going through that process wakes them back up. But I'm the kind of guy who pulls secondary harddrives while the system is running.
