Fedora 19 Administrator password

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http://forums.fedoraforum.org – To modify a user in Fedora 19 I need to provide the Administrator password. My root password doesn't work. It seems to be related to another issue. I cannot log in through the login screen. I have to do CTRL+ALT+F2 -> login -> startx. I'm in after that. However, when I lock the screen I cannot log in back. I'm getting the same authentication error as with the Administrator account. (HowTos)