I am running Debian Squeeze. I installed and removed Gnome3 and reinstalled Gnome2.x (epic fail and stupidity) and in the process I have lost audio, lspci returns following   # lspci | grep Audio00:1b.0 Audio device: Intel Corporation 82801I (ICH9 Family) HD Audio Controller (rev 03)   But lsmod doesn't return any thing.   $ lsmod |grep audioAny idea what could be wrong? Here is an update, I tried to install whatever possible package was removed by studying /var/log/dpkg.log. This fixed my other issues like no right click on desktop and blunt looking buttons etc. Now I have everything in order but sound is missing. I don't see sound section in gnome-control-center. Here are some findings:   kumar@debian-box:/$ lspci | grep Audio00:1b.0 Audio device: Intel Corporation 82801I (ICH9 Family) HD Audio Controller (rev 03)kumar@debian-box:/$ lsmod |grep audiokumar@debian-box:/$ lsmod |grep snd  kumar@debian-box:/$ lsmod |grep soundkumar@debian-box:/$ cat alsa-base.conf# autoloader aliasesinstall sound-slot-0 /sbin/modprobe snd-card-0install sound-slot-1 /sbin/modprobe snd-card-1install sound-slot-2 /sbin/modprobe snd-card-2install sound-slot-3 /sbin/modprobe snd-card-3install sound-slot-4 /sbin/modprobe snd-card-4install sound-slot-5 /sbin/modprobe snd-card-5install sound-slot-6 /sbin/modprobe snd-card-6install sound-slot-7 /sbin/modprobe snd-card-7# Cause optional modules to be loaded above generic modulesinstall snd /sbin/modprobe --ignore-install snd && { /sbin/modprobe --quiet snd-ioctl32 ; /sbin/modprobe --quiet snd-seq ; }install snd-rawmidi /sbin/modprobe --ignore-install snd-rawmidi && { /sbin/modprobe --quiet snd-seq-midi ; : ; }install snd-emu10k1 /sbin/modprobe --ignore-install snd-emu10k1 && { /sbin/modprobe --quiet snd-emu10k1-synth ; : ; }# Prevent abnormal drivers from grabbing index 0options bt87x index=-2options cx88_alsa index=-2options snd-atiixp-modem index=-2options snd-intel8x0m index=-2options snd-via82xx-modem index=-2# Keep snd-pcsp from beeing loaded as first soundcardoptions snd-pcsp index=-2# Keep snd-usb-audio from beeing loaded as first soundcardoptions snd-usb-audio index=-2Hope this helps in helping me. Its really hard for me to concentrate w/out headphones :(Last update, I fixed it using sudo modprobe snd-hda-intel, it seems I messed up kernel headers. 
lsmod |grep audio doesn't return anything?
debian;audio;alsa
Maybe you removed alsa related packages or you messed up their installation. Since there are no snd_* modules loaded, it's probable that /etc/modprobe.d/alsa-base.conf is wrong or missing. Try reinstalling alsa and reboot:apt-get --reinstall install alsa-base alsa-oss alsa-utils gstreamer0.10-alsaSometimes, upgrading a package, with many dependencies, to a major release version,   a lot of those dependencies might be removed and replaced with alternative packages. When downgrading to the previous release, it is not certain that the dependency chain will return to it's original state. Especially the upgraded configuration files.EDITSo, if you have upgraded from another repository than stable, like the experimental one, there is a way to downgrade all your packages to the stable release and hopefully fix all dependencies.Create a file /etc/apt/preferences and add the following contents:Package: *Pin: release a=squeezePin-Priority: 1001This is called pinning and it will give maximum priority to squeeze packages. Ensure you have squeeze repositories in /etc/apt/sources.list and runapt-get updateapt-get -d dist-upgradeapt-get dist-upgradeThis will downgrade every package to stable release. You have to be careful and watch the whole process, as all installation scripts are optimized for upgrading and not downgrading, this means that some packages may try to install in the wrong order. If that cause the downgrade to break, use dpkg --force-all -i /var/cache/apt/archives/<pkgname>.deb to force the installation of any required package, or apt-get -f install when needed and restart the dist-upgrade process.Remove /etc/apt/preferences at the end.