If your computer no longer plays CDs or DVDs or even recognizes them, you might want to try this quick fix. Usually, when this occurs, the CD/DVD drive isn't even recognized in My Computer (Computer in Vista). If this is so, double check the driver before you try this fix. Right-click the My Computer (or Computer in Vista) icon and select Manage... When the Computer Management windows appears, click on the Device Manager. If there are any yellow or red alert icons listed under Disk drives, then you'll have to re-install or update the drivers rather than trying this fix. However, if the 'Disk drives' key doesn't exist, then follow these steps:

You must enter the registry by clicking Start-> Run.. and typing regedit then hit Enter in XP and in Vista, click Start, type regedit and hit Enter. Once in the registry, BE CAREFUL and follow to this path:

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Class{4D36E965-E325-11CE-BFC1-08002BE10318}

In the {4D36E965-E325-11CE-BFC1-08002BE10318} folder, you will notice an UpperFilters and/or LowerFilters key. Delete these two (or one) keys (right-click, select Delete) and restart the computer. So long as the hardware itself isn't defective, your CD/DVD drive should be listed in My Computer (Computer in Vista) and your computer will read CDs again. I've seen this work more than 10 times, so long as the issue is not hardware or driver related.