gdm only displayed on half the screen

[Job Evers]

I recently restarted and when I did the graphical login screen was 
messed up.  It looked like it was configured to display on two monitors, 
with the username and password entry fields on the far right part of the 
screen.  Fortunately I can still log-in, and when I do my desktop gets 
set-up just fine.  Any thoughts on why gdm might be acting like this?

Thanks.