itunes does not see my cd drive

My iTunes installation used to show my CD drive in the left column when I inserted an audion cd into my drive. Now, suddenly, it does not. I can force iTunes to play the audio file on the cd but when it finishes playing a tune, the next tune up always is selected automatically from my Music Library. Very annoying. How do I get iTunes to see my cd drive and list it in the left column?

Thanx .