My VLC either does not show video or does not have sound

[neroh]

Last night all my mkv files stopped working on my vlc. I tried switching versions and then going back to a later version but nothing works. I do not know why this is happening. The latests version does not working properly and the previous does not work either. I am not sure as to why it so suddenly stopped working. All the codecs are the same, some of the mkv files work. But have stopped working. How should I fix this problem?