I really have to say that it's very likely that your filesystem has been damaged or the upgrade really hosed key system files. I would highly recommend backing up your files and reinstalling as when a system is in such a state it's usually too much hassle to pinpoint the problem.
To back up your files, you can download Ubuntu and use a LiveCD to mount your Ubuntu partition in the file manager. Navigate to /home// and your files will be there for the taking. Back them up to a thumb drive, wipe the computer and reinstall, then move the files back.
Another task that might be beneficial is to make sure that your hard drive is not failing. You can use Ubuntu's Disk Utility: Select your hard drive, then select "SMART data". Perform a short test and see if it tells you that the drive is about to fail (if it has a few bad sectors it's not worth fretting about as it's not uncommon).