I had to force shutdown my Ubuntu 12.04 64-bit, after which I restarted and tried to log in as a normal user, which was rejected several times. I then logged in as guest and
tty to my regular account with use of my normal password, which succeeded. (So the password is still valid.)
How can I gain access again via the normal login procedure (welcome screen)?
When I tried to log on with my new password, it again was denied. When I deliberately tried to log on with a faulty password, an error message came back, saying:
Access denied - wrong password.
I suppose, the first time the password was not rejected, but the procedure was aborted for some reason.
Some additional info after trying to find a solution: I am conviced it is a Compiz-issue. Why? before this happened, all sessions came to a grinding halt, regardless of being logged on in a 2D or 3d environment. I found a link saying that I should remove Compiz and proceed in a 2D environment, which initiall worked without a glitch, until my system went into a state of total obivium. Only after that, the above mentioned troubles appeared. In the meantime I have happened to find a thread with reference 17381, describing exactly what I have experienced. For now, I will try to cure this situation (later this week) and revert with the results, hopefully to close this post.
In the meantime I cordially thank you all, even if you didn't kill the problem; you gave me the inspiration to look further and find a possible cure.
Update2: After 15 hrs of trial-and-error I callled it quits (When I decided to tackle this problem, I've given myself 12 hrs, to avoid massive loss of time.) I decided to re-install Precise, since the "point 1" version has become availabe. Log-in is back to normal, as is the graphic environment. Response to mouse input is stil appalling, especially when I have a series of screens open as "children"of a "parent" screen. It still completely locks up. I have installed Enlightenment, Gnome classic, Gnome 3, Cinnamon and they all behave in a similar fashion.
FOR THOSE WHO NEED A WAY-OUT IN SITUATIONS OF THE LIKE: Open a terminal with [Ctrl+Alt+F2]. Type [sudo killall Firefox] (or whatever application you wish to terminate). Key in your password. Return to your graphical screen with [Ctrl+Alt+F7], and Bob's your uncle. Just re-open Firefox like nothing happened.
Next time you are stuck: [Ctrl+Alt+F2], upward arrow till you meet the command of your desire, [Ctrl+Alt+F7], etcetera. Hope this is of help. My next move will be to upgrade the kernel to 3.4 from the repositories for 12.10. However, since this entails a totally new situation, I will start a new thread on this site to avoid topic pollution
I will keep you posted. Still.