I am running Ubuntu 11.04 64bit with a ATI RadeonHD 5750/5770 (JUNIPER), 4GB ram. When I get to the login screen, all I see is a flickering white box instead of the login dialog.
The background displays fine. My hunch is that this problem is not related to the video driver, since I've reinstalled xserver-xorg-video-radeon and deinstalled fglrx.
I deleted the xorg.conf and tried different configurations, all with the same result. This only occurred after a recent update - though I don't know which packages got update. Any ideas?