No audio when using youtube

When I stream those youtube videos, the video looks good, but no sound.  Other programs in my system like MPC, winamp, etc. are fine with audio (with the correct codecs installed).

What's the deal?  I even reinstalled Macromedia, but the problem still exists.  Can anyone plz help me out?  TIA!

Did you check all the volume sliders in Volume Control?

Control Panel -> Sound and Audio Devices -> Device Volume/Advanced button

Make sure all the relevant sliders are showing in Volume Control (Options -> Properties). Check if anything is set to Mute and if all the sliders are high enough.