video, no audio

I have XP SP2, Real Player 10.5, Media Players 6.0 and 9.0.00. and VLC. I have a couple mpeg files which have video but no sound in all of these players. Most of my mpeg/avi clips play fine. I could also use tag 75 (where can I download it? I can’t find it anywhere). Thanks.
rjc739@verizon.net