Is it a CD or DVD in the drive? If it's a DVD and you have a CD ROM, it's not going to.

Is the disc scratched or smudged? Try wiping it off with a soft cloth and a few drops of water.

Does the drive show up in my computer? If not, check the cables.
 

rockyjohn

Distinguished
As always, Aford has the questions off to a good start. I will add a few:

Has it recognized CD's before? Any system changes since then?
Have you tried another CD - in other words will it not recognize any CD or just this one?
If just one, have you tried it in a known working system?

If none of the above, please report operating system and drive make and model.