Is this the Dell Dimension 2400?? Check in Device Manager. You may need to re-install the sound driver.
See an old post of yours. Check the last reply by flavallee.
http://forums.techguy.org/windows-xp/799086-xp-home-video-sound-problem.html
See an old post of yours. Check the last reply by flavallee.
http://forums.techguy.org/windows-xp/799086-xp-home-video-sound-problem.html