How do I get the GUI to come back?
This may not serve as an answer (but I can't comment yet):
when u login on terminal type startx and see if that starts GUI for you or as Roland said try sudo start gdm
Once your GUI starts you can provide more details easily as Oli is expecting to fix starting directly in GUI.
If none of those work then you may have to work on terminal and provide more details.
Best luck :)