Yesterday I ran the upgrade to 11.04 from 10.10. While it was configuring the packages, the display froze (as it was configuring libatm1, not that that necessarily matters). Apache and SSL weren't responding either, so I assumed it was a panic or something.
I restarted the machine and got this error. Followed the advice there, and now the machine boots and all, but at first after displaying plymouth it would show all the startup statuses and hang after "Starting AppArmor [OK]" or "Setting sensor limits [OK]" or "Checking battery status [OK]" (all approximate quotes). After some looking around, Xorg logs mentioned a segfault, so I removed and re-installed the windows server. Now it boots into a blank screen: no plymouth, no nothing. But Apache, SSH, and AFP via Netatalk work just fine.
Unfortunately I don't have access to the specs of this machine for now, but I do know it uses an ATI Radeon ####.
I don't think I have sufficient education to ask a better question than: is there a way to completely reload the GUI portion of 11.04?