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" botton on your controls. Look for the mute button and click it. Hopefully this is all that's wrong.
if it is old
...that could be the problem. My CyberHome DVD player, after lots of service, sometimes would play DVD 's without the sound . Usually after resting (turned off, and maybe unplugged) it would play sound again, for a while.
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