Probook 4530s (Win 7, 64-bit) - suddenly stopped playing sound from the internal speakers!

Hi all,

Recently I was watching youtube video on the laptop and the sound from speakers just gone! Just like someone disconnect the speakers, sound silly, I know Image may be NSFW.
Clik here to view.

I restarted the the laptop then, but speakers are still not giving any sound at all. I can only hear the sound coming through the connected headphones.  I checked all the drivers and everything seem to be fine. Here is a screen shoot from device manager:

http://s27.postimg.org/t4q9r8toj/devicemgr.png

I don't understand what is going on? Is anybody experienced this issue before? How to fix it? Thanks in advance