I was playing around with switching ttys. At some point, I locked my screen (CTRL + ALT + L) to switch user, and logged in to Guest. This opened up in tty8. I switched back to tty7 and logged out of my account, switched to tty8 and logged out of Guest.
I can no longer log into my actual account, but I can still log into Guest. I've restarted my computer, but I still can't log in.
I think the problem MUST lie with the tty switching, since nothing else I was doing was out of the usual and this has never happened before.
I'm using Ubuntu 12.04 on a ThinkPad W530.
UPDATE: I was able to create a new administrator account and log into that, so I still have access to all of my old files.
When I try to log in to the old account, the screen goes black for a second and I am returned to the log in screen.
I am able to log into my old account through tty1 and have access to everything.