Why can't my computer play the spoken words on a DVD?

When I play a DVD or practically any video file (ie- AVI file), my computer will play the music and background noise but not the spoken words. If it does play the spoken words, they are at an exceptionally low level or even completely delayed. I have tried playing the same files on my laptop and they work fine. I'm running Windows XP. Could it be my sound card? It is a Sound Blaster Live! 24-bit sound card that was installed about 4 or 5 years ago. Any thoughts?? Thank You!!!!