I have tried all the usual fixes from a million different forum posts..installed alsamixer (and checked it), pulseaudio, etc..
I will send all requested outputs and system settings.
Thank you all!
I apologize for this imperfect answer: I experienced the same problem on a HP Pavilion Notebook with Ubuntu 16 LTS in a dual boot with Windows 10. Following the instructions I found on the web : https://itsfoss.com/fix-sound-ubuntu-1304-quick-tip/ no sound on ubuntu 16.04.In setting it says dummy sound I have not been able to solve the problem and I remained persistently with a "Dummy output" for the sound. I realized that the sound was also desactivated under Windows. When I de-installed the provided audio driver and installed the Realtek one : https://realtek-download.com/wp-content/uploads/2017/08/0008-Win7_Win8_Win81_Win10_R282.exe, the sound was working again and switching back to ubuntu, an audio output was now present and the sound worked.