Re: Cannot upgrade from 11.04
Support for 11.04 has ended, which is why you can't contact the repositories.
You can always do a semi-clean install from the Ubuntu 12.04 or 12.10 CD: boot the CD. run the installer, use the manual partitioning screen and tell it to install the / to the current / location without formatting. This will preserve your files in /home even if it is on the same partition as /
That's what I would recommend.
I try to treat the cause, not the symptom. I avoid the terminal in instructions, unless it's easier or necessary. My instructions will work within the Ubuntu system, instead of breaking or subverting it. Those are the three guarantees to the helpee.