It's probably Unity or some other dependency of it. Unity is the graphical user interface for Ubuntu, and it's clearly pointing to the wrong... Everything.
You should still be able to jump to another tty screen (another terminal interface) by using
Ctrl + Alt + F6
You can use any of F1-F6, they all have separate terminal states respectively. Remember this utility when the GUI fails.
From the terminal, login with your username and password, then type
sudo apt-get update
sudo apt-get install --reinstall ubuntu-desktop
Breakdown of commands with quick references. If you don't know what the code is you're entering, you should always find out first, as a principal. This promotes learning, and system stability.
"sudo" - admin command, if you run this before anything it will grant you root privileges when running the command (requires root password)
"apt-get" - this is a package manager application, use it to manage software and git repositories. Very multifunctional.
"apt-get update" - updates the repositories and gets a list of any and all new software to be downloaded.
"apt-get install --reinstall" - full command broken down, apt-get (application), install (command to application, tells it to install a package), and --reinstall (optional command tagged to the install command. Reinstalls the specified package)
"ubuntu-desktop" - contains many different software packages related to the Ubuntu desktop, and GUI.
I see that comment now. I never had a problem with virtual box, you should try it if this doesn't work.