When I boot up my ubuntu 9.10 distro, the sound works just fine, but hen I sign into one of my profiles, the screen flickers for a second, and then the sound card no longer works. It appears that my profile is trying to reload my sound card and is confusing it. I have been unable to find out when it is loading the second instance though. Any help would be greatly appreciated.
There's a wonderful sound troubleshooting guide in the Ubuntu documentation that should better help you track down exactly what might be causing your trouble.
Personally, my issues with sound usually revolve around different processes trying to directly access my sound card at the same time. I used a utility called
randomsound to gather entropy for my system, but this would hijack my sound card and prevent PulseAudio from using it. Once I removed the conflicting application, everything worked as expected.
Hope that helps!
That seems to be a common issue for 9.10 distro, as I experienced the same some time ago.
What I did was to install the new version (10.10), which you can already do. But meanwhile I was stuck in that problems for a while.
If you are using alsa (as I guess), you can try to restart alsa by dropping the next in a terminal:
sudo alsa force-reload
Which will kill your current alsa audio session and start a fresh one, this way you can continue working and you can do it as you need it.
I know this is not a final solution but it worked for me at least for more than a year until I opted to reinstall and upgrade.