Usually, the graphic subsystem (the display manager,
or DM) is started up as one of the last items in the /etc/inittab
Exmples of DM's include KDM, XDM, and GDM.
If you cannot log-on graphically as root, it is because the display manager
has been told not to allow it. This is a configuration-file option that you can change.
But... you might not want to. You know, plenty of things are easy
to do in a graphical environment, and the computer will do anything
that root commands it to do, without waiting for ..
You have been warned.