The speaker suddenly loses its sound. In order to get back sound, I need to switch from analog to digital output, then vice versa.
I also did the suggested workaround on this website Resolve nosound problem on Ubuntu 13.04 Raring Ringtail,12.10 and Older
But the problem still unresolved.
I have no problem with the previous Ubuntu versions, just with 13.04.
Thank you in advanced.