I had a problem when I try to update my ubuntu "12.04LTS": Accidentally I turn off my computer, while the update was running. When I turn it on and try to complete the update, he always told me, that it´s a problem with the "apt-get". I just decide not to install it and then I couldn´t start my ubuntu any more, I always come in a point at the beginning like a terminal, where I have to give my username, but I forgot it. Any suggestions?! Thanx!.J :)
Boot into recovery mode command line and have a look at the directories under /home
The directory you see there will most likely be your username. If you've also forgotten the password you can reset it by following the instructions given in this question.
To repair the broken upgrade try the following: