I'm no expert, but until some Linux genius comes along I'll see what I can do.
1. Can you copy and paste the contents of the /etc/fstab file here for us to look at?
2. What kind of error does it give you when you try to edit the file? Not found? Permission denied?
Are the rest of the files in the /etc/ directory still there? (I don't expect you to know all the files that are supposed to be there. Just make sure the entire directory isn't empty.)
3. (Forgive me for asking an obvious question...) You weren't trying to mount a regular audio CD, were you? Regular audio CDs don't need to be mounted for you to play them. Plus, many audio CDs you buy in stores have copy protection that can 'confuse' your CD drive. That could be what caused the lockup.