I suppose it's just what you see when X11 fails to start during the boot procedure. I just had the similar issue but it had nothing to do with my chipset or else graphics card. I went to the terminal with Ctrl-Alt-F1 and made some attempts with the startx . I did have a cluster of fglrx issues from my nVidia graphics card, but under that was an error concerning being unable to write a keyboard configuration file.so as I found from some sources , it came to my notice that I was out of disk space. Freeing up some resolved the issue completely in my case. I think the nVidia issues were just since it was scanning every PCI port for devices.

I also have some more information as some guys have issues regarding lightdm and lightdm-gtk-theme. And all is sorted out as installing gdm package will assist .in addition, You need to run dpkg-reconfigure gdm. This will completely resolve your issue of lightdm.

Ubuntu má "recovery mode"
http://1.bp.blogspot.com/-DAoIzD2ZBjM/TtZHYBNRP1I/ AAAAAAAAFCs/nVg15g46Zno/grub2_picture.png