I have an NEC 6650A that has just stopped playing audio for no reason that I can find. Please any help would be appreciated. All mute boxes are open and the volume is up. My music files and e-mail are all fine. Just the DVD.

Did you installed the drivers or did you correctly set-up the DVD on your PC?

If you have only one CD/DVD Player/Burner, then set behind the drive, to the
Slave option. if you have more than one, then decide wich is the most used
one and perhaps set it to Master option.

Other than that, it's maybe a problem somewhere in your registry. Go to
Device manager and see if your device is working properly. If not, fix it.

or maybe, try just to put some earphones/headphones in the DVD and see
if you can hear noises.... anyway... try something.

If NOT, go to google and type in your model name and search for possible related problems or something...

Good luck!