The errors I get say there are problems loading the Nvidia kernel modules, but I tried purging the Nvidia drivers also with no success. Is there a way to completely restore Xorg configuration to default?
The only thing that ended up working for me was completely reinstalling Ubuntu. Even then, though, I still got this same error. It wasn't until I wiped the ~/.config directory that I was finally able to log in. The cause of this problem remains a mystery.