Let me just start out by saying I don't have much information on this issue considering I don't know what happened or why it happened. Not long ago I was able to click on and play .mkv files like any other normal video file but for some reason any .mkv file I have on my computer looks like this now:

and I can't even open them in Windows Movie Maker even though I used to be able to in the past..
I don't know what wrong or what changed, so that's why I mentioned I don't have much information. Can anyone please help me out? I don't know where to start...