I see the log-in screen but when I select one and enter the password it fails to log me in. It easily enters into guest account by the way.
I suspected there is some graphical problem and checked Xorg log. There it couldn't access fb0 for permission problems.
I should note the problem started happening when I updated Ubuntu from 14 to 16.
I also looked at kernel log and noticed some problems there. So I started a new thread here which didn't get any response.
So I uninstalled and re-installed lightdm and Xorg and Ubuntu-desktop with no success.
Any idea on how to investigate the matter?