In FEdora 12 by default your not allowed to login with login root in Gui mode . normally your can login with nurmal user and then from hsell your to su – root.
login with normal user this is a security settings policy in Fedora 12 , but there is way to force the system to permit you to login with root access , but still not adviced to login with supper user mode because its easy to dmanage the system with this user .
Now under root shell
su – root
findauth required pam_succeed_if.so user != root quiet
and comment it like this
#auth required pam_succeed_if.so user != root quiet
comment the same line in this file /etc/pam.d/gdm-password
save and exit
Now reboot your machine and login with the root user