Reboot PC, GNOME Shell login option gone

Hello Ubuntu Forums!

I just reboot my PC, and for whatever reason my GNOME Shell login option is gone. All thats left in the list is GNOME Classic and User Defined Session.

Before rebooting, nautilus had crashed, tried the ol' turn it off and on again, just to come back to GNOME Shell being gone.

Before nautilus had crashed I was playing around with MAME and XMAME. Not sure if that helps at all, but maybe it will!

Anyways, I'd like to know if GNOME Shell is gone, or theres just some setting I need to change to bring it back.

Im on Ubuntu 12.04, and it was GNOME 3.4.