Was having the same problem a few days ago after upgrading to 14.04 from 13.10, lost all sound. I did manage to get it working again and I believe the issue was with pulseaudio. Although I'm not really sure what it was that made it start working I do remember some things.
Verify first your card is recognized and are getting sound through alsa
In my case my onboard card (HDA Intel MID) and (HDA Nvidia) HDMI were being recognized and I was able to hear the 'front center' voice.
I also remember purging pulseaudio
and it giving an error about some dir not being empty so it was not removed. I manually deleted the files and directories it gave messages about
sudo apt-get purge pulseaudio
then delete your local config files,
rm -r ~/.pulse ~/.asound* ~/.pulse-cookie
reboot just incase
sudo apt-get install pulseaudio
hope for sound!
I also remeber not having a sound indicator at one point, if this happens make sure the package "indicator-sound" is installed.
Not being to hear the test sounds in the sound panel, make sure "libcanberra-pulse" is installed.