My Windows media player does not recogize cds when inserted

Are there any CDs that work correctly in your drive? Is this problem Is the problem also occurring for DVDs, or only CDs? And what type of CDs are you attempting to play?

Some internal devices get finicky if you're trying to read from a CD-RW or even some cheap brands of CD-R. You can try running a CD Lens cleaner, which is a Compact Disc with a tiny brush on it that is designed to remove dust and debris from the lens of the drive, but they're not always terribly effective.

It may be worth trying the same function from within Safe Mode (or Safe Mode with Networking) to see if the problem is related to software running on your PC, but if you're still seeing the error message in Safe Mode then the problem is either related to the drive (they do go bad) or a mis-configuration of Windows.

The other thing you could try is attempting to create a bootable CD, like a Linux Live CD (using another computer, if you have one handy) and booting to that. If you're able to boot successfully, chances are the problems are software (Windows) related, and not hardware related.

If you don't have access to a friend or another PC, you might try a restore point (if it stopped working recently). Or, if you're in the mood, a system reload. Seems like overkill for most scenarios, but some people run light builds on their PCs, so I'm just throwing it out there.