Yo Khan - I figured it out.
I'm using Windows XP OS.
Under Control Panel, go to Sounds and Audio Devices. Click and look at the top set of Tabs. Click on Audio tab. You will see 3 separate settings for sound devices - Sound Playback, Sound Recording, and MIDI music playback.
Click on Volume for Sound Playback, turn it up.
Click on MIDI music playback, turn it up.
Ignore the volume on Sound Recording unless you use that.
Click OK to save new volume settings.
Double check your sound setting if you have that icon on your desktop bar. Turn it up.
I played a youtube clip posted here (Parenthood movie clip) that used it be very muted. Not any more.
Did that work for you?