I need help with my VLC player

I was also facing a similar issue with my VLC player and I was not able to play .mkv files.

All you have to do is to right click on mkv file and select ‘open with’ from the shortcut menu.
Then choose default program and in the options dialogue box, check the “Use this app for all .MKV files” and then select VLC player.

It should play now. It worked for me, may it will work for you too.