We need more details. Are you using mac or pc? How did you transfer the video to your iPod? Did you test the video before transfering to the iPod? Try playing it on your computer using QuickTime player or VLC.

I only have an iPod shuffle & my partner also doesn't have a video compatible iPod. But I would always test all files before copying to an iPod. The video may have its audio in a format iPod doesn't understand. Thus you may need to convert it in such a way the audio is in a format iPod can understand. Did you see the link to the iPod forum from the Sticky about iTunes/iPod? That might be a better place to ask.