After updating to a new version of Ubuntu, you might have sound problems. Sometimes, Ubuntu doesn't recognize your audio devices and the only option available in the Sound Output settings menu is a dummy output. To fix the problem on your computer requires troubleshooting to identify what is causing the problem.
The Linux kernel needs the proper drivers for your audio devices in order to load the devices when your computer boots. Ubuntu does not install proprietary drivers by default and updating might have disabled the drivers you previously used. In the System Settings menu, click "Additional Drivers" to see what is available for your system. If proprietary audio drivers are listed, install them and reboot your computer. If there aren't drivers listed, open the Terminal and run "sudo lshw -class multimedia." You will see a list of the devices on your machine. If any are listed as "UNCLAIMED," it means that you don't have a driver installed. Search online for a Linux driver for your audio devices.
Ubuntu uses to packages to power sound. The Advanced Linux Sound Architecture (ALSA) is the underlying audio system. On top of if, Pulse operates. Sometimes when you update to a new version of Ubuntu, Pulse doesn't work properly as the sound configuration file gets corrupted. In the Terminal, run "mv .pulse .pulse.old" to rename your .pulse folder. You can do this from the graphical user interface. The folder is hidden in your Home folder. Press "Ctrl" and "H" to reveal it. When your computer reboots, it will create a new .pulse folder, with a new configuration file.
Sometimes, the problem is not with Pulse, but with ALSA, which requires troubleshooting on its own. Make sure that ALSA is installed in the first place by typing "sudo alsa" at the Terminal command line. This doesn't do anything other than let you know if the package is there. If it isn't, install it by running "sudo apt-get install alsa-base alsa-utils." If Alsa is installed, run "sudo alsa reload" and reboot. If ALSA still doesn't work, open Synaptic and type "alsa" in the Search field to see a list of ALSA-related packages. If you see any packages with "alsa" or "asound" listed as previously installed, mark them for re-installation.
If you still only have a dummy output available for your sound devices, then ask the Ubuntu community for help. Fixing audio problems is one of the more difficult troubleshooting tasks in Ubuntu and usually requires an experienced user to look at the output you get when running specific commands in the Terminal. Finally, you might have found a bug. Search Launchpad for similar problems specific to your hardware. If you do not see anything posted, you can open up your own bug report for assistance.