Why would a DVD player have no sound?

If it's new then it could be hooked up wrong. If it isn't new then you could have done what I did by mistake and hit the "mute" button on your controls. Look for the mute button and click it. Hopefully this is all that's wrong.

If it's old...that could be the problem. My CyberHome DVD player, after lots of service, sometimes would play DVD 's without the sound . Usually after resetting (turned off, and maybe unplugged) it would play sound again, for a while.

You could also try this:

For a CyberHome DVD player that plays no sound when watching DVD's, another option that worked for me without resetting it or shutting it off was to place a music CD in the player. Once it played the music CD with sound, eject it and put the DVD back in. Works without fail unless the sound is really messed up.