On screen keyboard malfunctioning on login screen

Recenly a friend of mine reported a similar problem which was due to "mistakenly" turning on the screen magnifier and on-screen keyboard from the accessibility preferences. Apparently this is a known bug.

If this is (a part of your problem) you can try out the fix recommended here.

Assuming that you do not wish to actually uninstall the screen magnifier or on-screen keyboard, here are some commands to disable them in GDM.

If you are able to log-in to the desktop, you can run them from a terminal or press Alt-F2 to get the run dialog, check "Run in terminal" and enter the commands there.

If you can't get to your desktop, press Ctr-Alt-F1 to drop to a console, login, enter the commands. You may have to restart to see the effects.

Disable screen magnifier in GDM:

sudo -u gdm gconftool-2 /desktop/gnome/applications/at/screen_magnifier_enabled --type bool --set false

Disable on-screen keyboard in GDM:

sudo -u gdm gconftool-2 /desktop/gnome/applications/at/screen_keyboard_enabled --type bool --set false