Thanks for your answer.

I'll try this solution next time (hope not).

Few days ago i followed the Sound Troubleshooting Guide below
https://help.ubuntu.com/community/SoundTroubleshootingProcedure

and the sound worked when i run

sudo add-apt-repository ppa:ubuntu-audio-dev/ppa; sudo apt-get update;sudo apt-get dist-upgrade; sudo apt-get install pavucontrol linux-sound-base alsa-base alsa-utils gdm ubuntu-desktop  linux-image-`uname -r` libasound2; sudo apt-get -y --reinstall install linux-sound-base alsa-base alsa-utils gdm ubuntu-desktop  linux-image-`uname -r` libasound2; killall pulseaudio; rm -r ~/.pulse*; sudo usermod -aG `cat /etc/group | grep -e '^pulse:' -e '^audio:' -e '^pulse-access:' -e '^pulse-rt:' -e '^video:' | awk -F: '{print $1}' | tr '

' ',' | sed 's:,$::g'` `whoami`

and restart the machine.

Thanks again!