Maybe your version of Ubuntu has passed end-of-life. Maybe it is still experimental. That is why I'm asking for the version number. Please post the output of this command!
Originally Posted by daviddixit
What happens if you run this command?
If still no go, try according to this list of commands originally posted by oldfred
sudo apt-get dist-upgrade
# This will reinstall if not current. (from my chroot procedure which does not have sudo on every line,
# so use the sudo -i first).
#if not chroot use: sudo -i
apt-get autoclean # only removes files that cannot be downloaded anymore (obsolete)
apt-get update #resync package index
apt-get upgrade #newest versions of all packages, update must be run first
#would upgrade you to the latest kernel in the repositories
#dist-upgrade is also able to remove existing packages if required
# fix Broken packages -f
sudo apt-get -f install
dpkg --configure -a