1. could be a hardware failure.... If possible, update the bios on the dvd drive. $15 dollar investment could fix that problem.
2. Update the kernel source and recompile. Could be possible you updated the system that's not compatible with your current configuration.
3. maybe /dev/cdrom needs to be linked to the correct device. This old site explains what I'm trying to say.

http://aplawrence.com/Bofcusm/1827.html