Troubleshooting Gnome/GTK

[Ken Barber]

Hello, are there any Gnome/GTK wizards on this list?

Something went horribly wrong this morning with the new install of FC3 on my 
son's computer: nothing that uses GTK will work.

On boot, or when exiting a session, this message appears on what should be the 
login screen:  "The greeter program appears to be crashing.  I will attempt 
to use a different one."

When trying to log in using GNOME the following error appears:  "Your session 
only lasted less than 10 seconds.  If you have not logged out yourself, this 
could mean that there is some installation problem or you are out of disk 
space...."

There is a checkbox that allows viewing of ~/.xsession-errors -- checking it 
reveals nothing interesting, only this:

[first line:]
/etc/X11/gdm/PreSession/Default:  registering your session with wtmp and utmp
[second line:]
/etc/X11/gdm/PreSession/Default:  running:  /usr/bin/X11/sessreg -a 
-w /var/log/wtmp -u /var/run/utmp -x "/var/gdm/:0.Xservers" -h "" -l ":0" 
"root"
[third line:]
Agent pid 9172
[last line:]
SESSION_MANAGER=local/hostname:/tmp.ICE-unix/9684

This happens no matter who tries to log in to a GNOME session (even root).
We can log in to KDE sessions but nothing that relies on GTK (such as 
system-config-packages, which would allow us to remove and reinstall Gnome) 
works.

This is a fresh stock install that was fully updated last night.

It's probably not a FC3-specific bug because my install is working perfectly 
on similar hardware.

I presume there is a file somewhere that got corrupted, but running 'rpm -Va' 
produces a very long listing of dependencies that changed when prelink was 
run, and there's a lot to comb through there.

Is there anyone reading this who can tell me where to look next?

Thanks,

Ken