"We approached the case, you remember, with an absolutely blank mind,
which is always an advantage. We had formed no theories. We were simply
there to observe and to draw inferences from our observations." -
Sherlock Holmes
What happens when you try? The DVD and CD parts of a DVD/CD-ROM drive
use separate lasers. It is possible that the drive has failed. Without
more information from you, it is impossible to be more specific. Swap
out the drive for a known-working one; if everything works, discard the
faulty drive.