If you enable autologin and then disable it (using the Gnome control panel)
you will end up with a file /etc/sysconfig/autologin with a line that says:
AUTOLOGIN=no

The presence of this file at boot time causes the /etc/X11/prefdm script
(started by
/etc/inittab) to execute /usr/sbin/autologin, which reads the
"AUTOLOGIN=no"
setting and doesn't do anything, except return 0 (zero) to prefdm.

Prefdm considers a zero return value to indicate success, and therefore it
just
exits without starting a display manager.  This causes an init error at
boot time
and X never gets started.

THE FIX: make autologin return non-zero if it finds "AUTOLOGIN=no"
in its config file.