without more info there isn't to much to offer.If you have more info on the file (audio codec,video codec,Exact container format instead of just file extension) but flailing in the dark it sounds like a codec problem i' had quite a few of those originally windows media player is famous for it's lack of codec support AC3 filter fixed most of them so far but with out more info i can't suggest what you should down;oad. Have you tried any other players?