You can try to rebuild the database by deleting the old files.. Log into windows as the administrator then navigate to C:\Documents and settings\(current user_the name of the user you are logged in as_should be administrator)\Local settings\Application Data\Microsoft\ then right click on the "Media Player" folder and select delete.
Restart media player and media player should automatically rebuild the folder/database.

You can try this with WMP11 if you want to use it.

Here is a link to the instructions at support.microsoft.com