This is a very common problem.
A dvd drive is really a combination dvd-cd drive and they are essentially independent of one another so they can fail independently of one another.
Usually the dvd side fails first because it is built to much closer tolerances than cd so it becomes functionally a cd drive. So your operating system sees only a functional CD drive and functions accordingly.
Also sometimes only the ability to write fails first and the drive can continue to read.
They are cheap get a new one.
I'm well familiar with this because my work requires I keep running four DVD R/W drives at once. Right now one of my older DVD drives is starting to become flaky and loosing the ability to write in DVD mode.
Last edited by wildman; 04-09-2010 at 06:53 AM.