PC Internet sound

Hello,

I have a desktop computer with Windows Vista installed and when I open my Google internet connection I can run videos, i.e., Yourtube, but all of a sudden there is no sound.

When I open my music files in the computer I can run the music and it play just fine. It is only when I am trying to run an internet video that the sound won't work. I also have a laptop that in connected to the same modem and the sound works with videos on that machine.