Hi,
You may need to reinstall Media Player, but I doubt it.
First, I would try the procedure outlined at:
http://www.gamesforloving.com/phpbb2/viewtopic.php?t=344
I suspect that this may fix the problem. If it doesn't, try the procedure outlined here:
http://www.softwaretipsandtricks.com/windowsxp/articles/117/1/Delete%7B47%7DRepair-the-Windows-Media-Player-Library
After doing this, you will probably need to do the first procedure again.
If it still doesn't work, then you may need to reinstall media player.
Thanks,
Don