I'm running (well, at least I WAS running) Ubuntu 11.04 and slowly converting to Ubuntu Studio. I had most of the components running except for the audio portion. The system ran fine and booted normally. I loaded up the audio components to make jackd work - stopping before I got a chance to load the low-latency kernel - and had to reboot to Windows for a second. Upon returning to Ubuntu, I now get the Ubuntu Studio splash screen, the system gives me a cheery "ding", and then nothing - no login dialog to get me into the desktop.
I can ALT-F2 to get into a terminal. Gdm's processes appear to be running mostly. However, the last line in syslog contains a gdm error: WARNING: Unable to find users: no seat-id found.
Stopping and then restarting gdm has no effect. I have walked backward through the audio installation process removing the packages that were installed, also with no effect. I have been googling this for a few days. I would be ever so grateful if someone could at least point me in the right direction before I have to whip out the install disk yet again.