[CentOS] CentOS 4.5 system doesn't boot after installing latest updates

Mon Sep 24 19:51:57 UTC 2007
Alfred von Campe <alfred at von-campe.com>

Today I decided to install all the latest updates (including the -06  
kernel).  The "yum update" seems to have run just fine (no errors),  
but when I rebooted the system it just sits there with the word  
"GRUB" in the upper left hand corner.  I booted from the CentOS 4.5  
install CD into rescue mode, did a "chroot /mnt/sysimage" and  
reinstalled grub and the latest kernel, but it still gets stuck in  
the same place.  It's not that I can't boot the new kernel; I can't  
even get to the grub screen!

Any ideas?  I am totally stuck at the moment...