I had sound on initial install using an AMD quad core HP PC and after some problems with installing updates and using synaptic and updates sound want missing.
Almost 2 weeks of research and fixes with sudo apt-get commands in terminal using various fixes had no results.
Almost had to re install OS but I did download and burn Kubuntu, Xubuntu and Lubuntu as well as other Linux O S Distros. So I decided to use the ISO CD Roms to run from CD and check sound settings and files.
I noticed that my sound settings were dummy settings. NO SOUND. Alsa would not install and I saw no fix until I used:
sudo apt-get install NVidea MCP61 driver.
I then checked my home folder.
noticed some HTLM or HTM? files at the bottom of the page and deleted 3 script files that looked out of place.
After this I used:
sudo apt-get install update
after this I followed the suggestion on the terminal page for other fixes -f
I tried to reinstall
synaptic and went to the Synaptic package program there I noticed that one package was not installed , I tick and install one extra. removed one and reinstalled or upgraded one that had an exclamation mark next to it. Sorry did not pay attention to detail just went with gut feeling and from what I read.
02:30 am I waited to have all the packages install without taking notes so this is a bit sketchy. 03:00 last resort before reinstalling OS I turn PC off go to bed.
The next day I turn PC on and sound works.
HDMI/ display port
recovered in sound settings.
Dummy output gone.
Note. while using the CD rom to test sound with Kubuntu ISO DVD only the right speaker tested OK the left did not work, Ubuntu 12.04 same as Lubuntu. Did not try Xubuntu CD?
The package Manager error still exists and while trying to use package manager to install updates and upgrades previously kept giving me error 404, 502 and proxy error. Disabling Firefox proxy settings did not work?
Something else to spend a lot of time on.
Hope this helps.