How to (re)associate audio/video files with Windows Media Player 12?

Hi,
After unsolvable problems with VLC player (constant crash reports) I want to move back to Windows Media Player as my standard program to play audio & video files. But whatever I click and do, I cannot find a way to (re)associate the 'VLC'-files to WMP12.
If I rightclick a 'VLC'-file in a folder, I can select 'open with' and then select WMP. But only for one instance! If i want to make WMP the default opener, I get this error message: 'This file does not have a program associated with it for performing this action. Please install a program or, if one is already installed, create an association in the default programs control panel' - Strange message, because this file HAS a default program already, I just want to change it!
I have desperately been looking for an option Windows had in the past, where you can (in explorer, I think) get a list of ALL file extensions, then select which program to use to open a specific extension, then check the box 'use this program by default for this file type'. Is this management tool gone?
What to do?

But Windows Media Player is not in that list... although it HAS been installed and I can use it for playing back individual files...