is your machine a Dell? I googled and found the following:
http://forums.us.dell.com/supportfor...message.id=806
also another site suggested clearing the cmos on the motherboard. if you have the motherboard manual, follow the instructions to clear cmos. you may have to go back into bios and check settings after that. Sounds like you know what you're doing so give it a go!
If that doesn't work, if you can try another CDrom - or try this one in another machine. It may be dead!