How to install ALSA from scratch, Ubuntu 9.10

Hello guys,
I think this time I ruined my audio settings big time.
I started with a vanilla installation of 9.10 in December 2009.
At that point, everything was working fine.
I wanted to test some of the audio/video features of Empathy, so I installed some of the ppa packages associated with those functionality.
At that point something went wrong and I lost my microphone... I mean audio was working ok, but I couldn't get my mic to work. I tried installing ALSA mixer and some other tricks.
Then I gave up for about a year. Now I wanted to make my mic finally work, so I started by removing those ppa sources and trying to go back to the standard installation. It didn't work.
Then I followed the ALSA troubleshooting instructions:

https://help.ubuntu.com/community/SoundTroubleshooting

It didn't work, so I finally took the 'last resource' option of removing ALSA and installing OSS4...

That didn't work either.

Is there any way re-installing ALSA to the vanilla state?... in fact if I could reset the whole ubuntu back to standard 9.10 I would be happy.

Any ideas? (yeah, besides wiping the whole thing out and starting all over again... that one I know it will work, but there are several partitions, dual booting with M$ Windows, lots of data, etc)

I hope someone can offer a hint.

Regards,

Kiko