I just did a fresh install of 10.04 and I hate to say it, but out of the box is was harder to set up than its predecessor. The install went fine and it wasn't until I logged in I discovered I had no sound. I eventual found a setting (gnome-volume-control) that had a checked box next to mute. Bear in mind this was a fresh install and I had never opened this dialogue before.
I un-checked mute and had sound, but every time I logged out it defaulted back to mute. After a bit of searching the cure was to set the sound levels are required then run the following in terminal...
sudo aslactl store 0