Turn off the magnifier at the login screen.
Turning on the screen magnifier (part of the Accessibility package) Results in an odd condition in the log in screen that makes half the screen appear dark and makes it difficult to log-in unless you know what you are doing and what is going on.
People often turn this on without really understanding what they are doing and subsequently can't log in. Here is how to disable it.
This will turn off the screen magnifier
sudo -u gdm gconftool-2 /desktop/gnome/applications/at/screen_magnifier_enabled --type bool --set false
This will verify that screen magnifier is set to false
sudo -u gdm gconftool-2 --get /desktop/gnome/applications/at/screen_magnifier_enabled
Once you've done that, you can turn the rest off in the universal access menu.
You can also disable:
if they are causing problems. the former causes an onscreen keyboard to appear at all times.