Ok, I seem to have created a problem inadvertently. My .m4a files(you probably know what types of files they are--if not, just go Something it) set in my hard drive were always programmed to play in Windows Media Player. I had used a codec in order to do so.

Now for some reason(I believe it was either after an update or a deletion) my m4a's can't be played by anything. It's a blank thumbnail, no program icon to show as a default program, none of that. Pressing Enter does nothing, when I right-click on it and click Open with, no dialog box or anything shows up for me to choose the program to open it with. Going to the Default Programs feature, when I go to the m4a extension, the Default Program listed says Unknown Application. Nothing happens when I click Choose Program to switch it, again nothing happens.

I tried restoring my computer to my least recent version, but for some reason it failed!

What can I do?

It's Windows 8, by the way.