MPEG4 player plays some files, but not others

I have had my MPEG4 player for about a month now and am very happy with it. Two weeks ago I loaded some files on from my dad's computer. These files do not play on my TV: a blank screen comes on then a STOP appears in the top right hand corner and the file menu comes back up. These files play on my computer from my MPEG4 player no problem. The files are definitely on the player: the file size appears at the bottom of the menu when the file is selected. Also, files that I have taken from my dad's computer prior to these last two weeks do work. So the question is: is there something i can do, or some setting i can adjust to get these files to work?