Ok, let's try something else. Let's create a new user.
While logged as root, look for "Users and Groups" (in the menu, under "System Tools") and create a new user, give it administrative privileges (tick everything at "Advanced Settings"->"User Privileges"), then restart and try to log in as that new user.
If for some reason you cannot do it that way, then open a terminal and execute the command: adduser your_new_username, then usermod -a -G admin your_new_username.
Then try to log as that user, and if you can, go to "Users and Groups" and give yourself all the privileges and restart.
Sorry, I only speak Spanish