I realize this is very old but in case anyone does an internet search.. After trying all the "solutions" posted on various sites what eventually fixed it for me was..
Restoring defaults, restoring wmp as the default program for everything but mp3's. VLC player had become default for 1 or 2 of the file types long after it had been installed.
Tools > Options > Performance > Click Restore Defaults
Tools > Options > File types > Click The Greyed Out File Types
WMP now functions properly, for me at least
