Simpler way: while WMP is not
in use, type WMDB into the search bar, this will give you the database files. Delete them, open WMP, click F3 and media files will reboot.
BE AWARE this won't undo any tags - or undo any of the odd locations and library settings that WMP has already decided on (whether you like it or not). It will still continue to arrange the library how MSN wants it (not how you want it)