Media player does not recognise music and video as media files

Having recently had someone else using my computer for a while, installing various software (like winamp and SubEdit player) it seems windows media player (that's what I use) no longer recognises the usual files as media files like .mp3 .wmv .m3u .avi etc etc so when I click open file and select "media files (all types)" in the file type box it shows nothing, so I have to change it to all files which is irritating. Media player still plays everything fine but this is pretty annoying.

Any suuggestions how to reassign these files as media files ?