Today, on my Ubuntu 9.10 I was trying to watch a youtube video, unfortunately my flash completely freaked out and unfortunately there was no sound either. In the past I used to reboot my machine and then the issue was solved, however, since I had so many apps open, I didn't want to reboot.
So here's how I got it back working:
1. lsof | grep pcm
2. kill the results for pulseaudio and firefox
3. restart alsa: sudo /etc/init.d/alsa-utils restart
remark I killed firefox too because when I then restart firefox it asks me to restore the previous session, so I have all my pages (even in different windows) open again upon starting firefox
w00t, youtube, here I come !
However, if it's still not working after this, most likely there has been a kernel update. Then I used this procedure and then everything worked again:
This procedure might take some time (in my case appx 15 minutes)
This procedure could perhaps solve a lot of threads on ubuntu forums like "no sound in flash", "flash makes FF crash", etc...