Wont play .VOB files


i am in the process of converting all my files to .mkv formats since i have started doing this the files not yet converted which are currently in .VOB will not play

You follow the entire process and when you click play the time comes up and then it is black screen.

this is the second time it has happened in the last week

The only way to get it working again is by pushing the master reset button at the back of the device

any ideas why this could be happening??

I’ve read about this but I couldn’t reproduce it myself.  A similar bug I experienced was when fast forwarding (incl. 10 min skip)  too much in a VOB would suddenly make the player hang so that a reset was necessary.