Need to repair or reinstall Ubuntu 12.04 without losing programs or data

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http://askubuntu.com – I was trying to change the ownership on an external drive, and mistakenly used sudo chown -RL myuser:myuser /media/"New Volume" Unfortunately, it changed the ownership on the entire drive to myuser. I've since changed the ownership back to root on everything except the /home/myuser directory. But, I still have problems, such as google-chrome didn't work anymore, I can't see mounted drives, and pulseaudio doesn't work. (There are probably more--but these were enough to make me want to fix this). I downloaded the Ubuntu 12.04 LTS DVD (x86_64) and am booted into it right now. When I try to d (HowTos)