I am running RH9 with Gnome.

I started experiencing a complete hangup before the graphical login screen appears. I get an unreadable ASCII style Yes|No box and selecting either choice does nothing. I also can not ctrl-alt-f2 to a text terminal.

I don't have a boot disk (oops) so I booted with Knoppix and was able to chage the default runlevel from 5 to 3 in /etc/inittab. I still have the same problem, but now I am able to ctrl-alt-f2 to a text terminal and log in.

ps-ef show a process for [gdm-binary].

Does anybody have any idea what this could be? What I could try to fix it?

Why is gdm even loading at runlevel 3?

Have you checked your init.d scripts? Perhaps you have xdm linked into the rc3.d directory. grep xdm in your rc.d directories and see if you have xdm linked anywhere other than rc5.d

If you find that is the trouble, it would be a good idea to check the rest of the scripts. Consider if the wound was self-inflicted or whether you've been hacked.