If you encounter power outage or any other issue which causes your computer to power down abruptly while upgrading Ubuntu from one version to newer, you are more likely to get a broken ubuntu upgrade. This can be fixed if you are able to get to a terminal in the broken system.
sudo dpkg --configure -a
installs and configures any remaning upgrade packages
sudo apt-get upgrade --fix-broken
I encountered this issue while trying to upgrade from Ubuntu 13.10 to 14.04. This method fixed my ubuntu upgrade and saved me from a clean install. I hope this works out for others as well.