If you have moved your music around on your hard drives, Windows Media Player continues to add new entries into it's library instead of modifying the existing ones. This means that you will now have multiple entries for the same song, half of which will not work now because you have moved the files to their new location. To delete the current library and build a new one, do the following:
1. Close Windows Media Player, wait about 3 seconds for the database to close.
2. Using "My Computer", navigate to the following folder:
F (or whatever drive is appropriate for you):\Documents and Settings\All Users\Application Data\Microsoft\Media Index
3. Delete the "wmplibrary....db" file here. This is not your actual music, only the database which Windows Media Player uses as a listing.
4. Start Windows Media Player
5. Hit "F3" and enter the location where you have moved your music to. If it is on muliple drives, check "All Drives". Let it finish.
All the old listings will now be gone, and you will only have the new accurate ones.