I am new to Ubuntu so please be gentle.
I upgraded my Ubuntu 12.04 to 13.10 a few days ago. Everything was ok, I set it up according to my ideas and it worked as I wanted. Today, I worked under Windows and then I rebooted to Ubuntu and the problem came up (I have changed something, so I am not sure whether it has caused the problem or not). The login-screen displayed correctly but there was no input box for log in. I pressed arrow keys and the input box for remote login appeared, but no other. I tried to reinstall greeter or lightdm, but I don't understand theese things very well.