After about the second/third batch of updates on a fresh install of Ubuntu 12.04, I end up getting stuck in an infinite login loop: I enter my password, screen goes black and shows me the end of the initialisation messages (including things like CUPS initialising), and then the greeter reappears.

Kicker is, as I'm using gnome-shell, I just decided to uninstall LightDM, ubuntu-desktop and unity-greeter, using GDM as my manager, and the problem still happens in exactly the same manner.

I'm lost even as to where to start looking - Xorg logs, LightDM logs (before I removed it), syslog and dmesg logs have held no unusual information at all.

I have a TeX assignment due next week, and reinstalling Ubuntu every time I want to work on it is not going to work (nor is using TeX on Windows ;). Anything else I should try?