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!

Thanks for pointing that out.  But I have all those sliders in "high" mode already.  However, the strangest thing is that,

Control Panel -> Sound and Audio Devices -> Audio -> MIDI music playback

.. doesn't have anything selected as "Default device."  I suspect it's because of this.

So, I selected the "Microsoft GS Wavetable SW Synth" under the pull-down option, clicked Apply and OK.  Then I went back to that audio setting but it turns back to nothing being selected.  WTF?  Help!  Anyone, please!