Upgrade Ubuntu 13.04 to 14.04 LTS

1. Follow steps in 

http://www.tuxtrix.com/2014/03/upgrade-from-ubuntu-1304-to-ubuntu-1404.html
This is gonna take hours.
There are prompts you need to select when installing new packages, don't leave.

2. If Ubuntu 14.04 LTS boots to tty1

sudo apt-get update 
sudo apt-get install aptitude
sudo aptitude reinstall lightdm
reboot and see if it works, else
sudo aptitude install gdm
reboot