VLC has changed the way your PC opens files. To change it back you need to open WMP and click Tools>Option and then click on the File Types tab. Here you can tick whatever files you want WMP to open as default.
set the default to the player you will play the most in, and use a right click 'open with' for the others. Once you do this a couple times it will be in the quick launch list and not just in the browse section/