sudo is not working

Thank you for taking the time to report this issue and helping to make Ubuntu better. Examining the information you have given us, this does not appear to be a bug report so we are closing it and converting it to a question in the support tracker. We appreciate the difficulties you are facing, but it would make more sense to raise problems you are having in the support tracker at https://answers.launchpad.net/ubuntu if you are uncertain if they are bugs. For help on reporting bugs, see https://help.ubuntu.com/community/ReportingBugs .

try with the "su root" command; if you have set root password (that is not your user's password), you should be able to enter a root session; other way, you have to try with Ubuntu Recovery session; at boot, when GRUB is shown, select "Ubuntu [your-version] (recovery mode)"; if you have not set root password, it will not ask for it; if a blue meu is shown, choose "drop to root shell".

If none of this works, you will have to recover using a live cd and trying to recover in there.

My personal suggestion, based on my experience, is that if you have a place to store your files other than your main hard disk (e.g. an USB hard disk or a network storage), you can use a live CD to copy your files there, ant then format your system. That's what I'll do, if I were you. Recovering for such a mess can be difficult.

If you can reach a root shell, however, you may want to try "dpkg-reconfigure --all", which should, at least, make your system working again (my format suggestion remains, though)