Does sound work on other applications? What sound hardware is it? Which ALSA driver? Do you get channels if you run "alsamixer" from the command line? Oh, and does Ubuntu use pulseaudio or other audio servers like that? If so, does sound work when you disable those? I seem to think that there's some kind of "pasuspend" or something which you can use to temporarily disable pulseaudio, though I don't know the exact command.