someones_takako

I have no idea what I am doing. The sound is not on solo, the clips are not muted, the volume slider is all the way to the right, and my computer's sound is fine. It is this one mp4 file that won't play sound at all - others video and audio clips are included, and they work fine. It is an almost twenty minute video, and I would be so miserable if I had to re-import it all over again... I don't know how to restart drivers, and if that would help at all. Can anyone give me some help?