Solved Unable to associate file types with Windows Media Player?!

I'm in the midst of a weeks-long project to get every media type I can think of associated with the program that I prefer for opening it. (Let's just say it's tedious and get to the problem I'm having!) I've been using the windows "Default Programs" program, as well as "right click-->open with" on literally hundreds of file types and over a dozen programs, without issue. However, for some reason I can't get file types to associate with Windows Media Player. I can get those same file types to associate with other media players (which unfortunately don't open them properly), but not WMP.

When I open the list of all file types in Default Programs, I double-click on the file type I want; WMP isn't in the resulting list, so I go to "look for another app on this PC" and go to program files\windows media player\wmplayer.exe. When I select this exe, it goes back to the list of all file types, but the list doesn't refresh as it does when I associate a file type successfully to another program, and the file type is still unassociated. I've tried using the wmplayer.exe under the "program files (x86)" folder as well, with the same issue. When I right click on a file of that file type in Windows Explorer, I go through the same process; the file type isn't associated with WMP, and WMP doesn't open to open the file. I can open WMP and drag-and-drop the file into the window with no issues.

Anyone have any clue what could be going on here? Every other program I've tried gets associated with file types uneventfully, and this is driving me insane!

Ah! 20 minutes after asking I finally found the problem. Windows Media Player was unchecked in "Program Access and Computer Defaults." Once I checked it, all was okay again.

Windows Media Player - Restore or Remove from Default Programs