I tried updating via the "Software Update" GUI and always was stopped by a 404 error.

So, I then did the typical
Code:
apt-get update
apt-get upgrade
All seemed to flow well, skipping over a few errors and 404s occasionally. However, upon rebooting, I am not able to log in. The standard login prompt appears and I enter my credentials. Instead of popping to my desktop, the screen goes black (with cursor visible) for a few seconds before returning to the login screen. There are no authentication failure messages or anything else indicating an error, just a loop back to the login screen.

I have experience fixing things in recovery mode, but this time, I have no idea what I broke and where to start.

Kali 1.??? x64 Gnome

I cannot find login issues relating to an update. Tried rebooting several times and using the default password.