After the last update from Microsoft (september 2012), my Windows Media Player stopped responding… actually it starts up but it is just blank and nothing responds. The strange thing is that it does not also use CPU (0% utilization).
If this happens, best way is to use the MS Fixit tool located at:
http://support.microsoft.com/mats/windows_media_player_diagnostic/
Other options:
1) Reset Media Library manually
Close WMP12.
Type in %LOCALAPPDATA%\Microsoft in the search field, and press Enter Key.
Open the Microsoft Folder and locate Media Player and rename the Media Player folder to something like Media Player old.
2) Reinstall
via Turn Windows features on or off under the Control Panel.Uncheck Windows Media Player (under Media Features),follow on-screen instructions and reboot