I have 12.04 and I partially updated it from the update manager. It was showing me an option of update to 14.04 too. After the partial update I found, it removed my libreoffice and I can't open my files. It also removed the availability of update to 14.04 from the manager. I tried changing the source server from software centre but didn't work.
Now, after the shutdown, Ubuntu won't boot and leads to a tty1 login for a second before it hangs at 'system running in low graphics mode' error.
What should I do? I have certain data that wasn't backed up and I can't lose it!