Vera,
If you are trying to play a retail 'movie' type DVD on your drive, they use
a sound format called Dolby 5.1
A lot of older soundcards can't handle this format.
You can check for updates from the soundcard manufacturer, but it tends to
require a hardware upgrade.
If this isn't what you meant, post some more info about the discs being
played and your system specs.
Hope this helps,
Chek