HP touchsmart envy 20 sound not working

Hi,

The sound on my HP touchsmart envy 20 is not working. It plays systems sounds fine and when I do a test, the sound is ok. 

But when I try to play videos on vlc or youtube, no sound at all.

I am using windows 8.1, HP touchsmart envy 20, product number is H4G65AA#B4. Speaker driver version is 6.3.9600.16384. Tried several methods listed on this forum but does not work. my PC is 64 bit