I upgraded my ubuntu from 11.04 to 11.10 via mounting the latest alternate CD image released on Oct. 13 as the final standard version and running the cdromupgrade prompt successfully, with full latest upgrades installed before ending the distribution upgrading process and rebooting. After reboot, the new lightdm showed up as expected, and I could choose the login shell from a menu containing "ubuntu", "ubuntu 2D", "recovery console", "kde workspace", "cairo-dock with effects", "cairo-dock without effects", etc. next to my name which corresponds to my username.
HOWEVER, for example, I chose "ubuntu" (as the default selection) and input the correct (if not correct, the lightdm would ask you to input again, but it did not do so, I have tried) password and entered. The screen splashed to the black screen of the background text interface of gdm for a very short interval and then returned back to the interface of lightdm without my user account logged in and appeared as if I have not done anything on the laptop. Neither could I log in as a guest user as the same black screen splashed and lightdm reappeared.
Before the upgrade, I could run gnome 2, kde, unity all quite well on the laptop, but the status quo is that no one from the menu prompt beside my name can log in to my account, including the "recovery console".
Actually I can switch to the ttys and log in my account with my username and passcode normally, as can run all commands in the tty (I am currently doing this). I can also act like a superuser via the "sudo" command and get a # prompt via the "sudo -i" command, with the correct password, no problem.
In the root prompt, I can run "service lightdm stop" and "startx" to a root unity UI successfully (that is the way how this passage comes out), but in the $ prompt, after running "service lightdm stop" and "startx", it simply appears "No protocol specified" endlessly and no GUI appears.
I found the package "gnome-shell" not fully installed and fixed it, but it did not help, simply resulting in a selection in the menu which cannot access my account as its companions.
I have made all the packages in my laptop up-to-date and no updates should be installed.
My device is ThinkPad X61, with all its functions running well on all previous ubuntu distributions since 10.04 LTS. I had upgraded my os from 10.04 LTS to 10.10 in the way I performed today without any unexpected results one year ago.
I suspect it is the newly integrated lightdm that set these obstacles, and I want to get this bug fixed, please help!