This post was answered on 26 April. But, here goes:
On the top toolbar did you click View and check Full Mode?
If that doesn't work, then -
You may have corrupted some of the program files. You can try to
reinstall it overtop of itself. Do not delete current program.
WMP10 (12.2Mb) and older - OldVersion.com http://oldversion.com/program.php?n=wmp