Im a Music Technician for a college and in one of the Studios we have a Mac Pro running 10.6.6. It has been running absolutely fine until today, after a restart, the accounts had disappeared entirely from the Login window. If you click back you can select "Other..." but any information you put in is rejected (screen shake). This goes for the local accounts and the network accounts.
So I did some research and found that it is (was) a known problem and was fixed in the 10.6.7 update as found at the bottom of the bug fixes here: http://support.apple.com/kb/HT4472
I did some more digging and found several similar issues. One solution suggested that I set the root password (which I did via single user mode) and attempt to login on the root account and then go to System preferences and add the accounts back in one by one (they then inherit the old User directories and be running as it was before). However, root access doesn't work either! I know the password I am putting in is correct.
Another solution said about deleting .AppleSetupDone file so it goes through the whole welcome process and forces a new account setup (which it did but then went straight to login screen and same problem).
I've booted in Target Disk Mode and done Disk First Aid and stuff and everything appears to be ok (and as said in the beginning it has been running fine).
I've tried digging around myself via Target Disk Mode (checking for any suspect preference files, that type of thing) but unfortunately I am getting nowhere.
The only other option I see after this is to reinstall which I'd rather not do as there's a load of drivers and stuff for all the music equipment - ie its a bigger job than "just reinstalling".
Just throwing this out there in the hope someone might have a clue.
Just as a sidenote: I know in System Preferences you can deactivate the login screen and have the computer log straight into an account. Is there any way of making this happen via Single User mode perhaps? I'm clutching at straws I know