I have just recovered my Laptop from a GRUB issue now when I want to login, the screen splashes and go back to login screen, I can login fine using terminal, Some people say you need to reset unity but the problem is my WiFi don't work idk the reason. I tried to reset unity via Dconf reset -f /org/compiz command but it says: cannot autolunch d-bus without x11 $display
have you tried restart the lightdm service.
or u can do : apt-get install --reinstall ubuntu-session
as per this url:
and if problem still exists than try to login as a guest account, if succeeded than go back to ctrl+alt+f1 check the permission & ownership of your user:
ls -la /home/user
check optput of these files:
drwx------ 3 user user 4096 Aug 6 2015 .gnome
-rw------- 1 user user 49 Jan 1 2010 .Xauthority
if permission are not like this than set the permission and also do chown to user for all files in the user & reboot system, hope this will solve your problem.