just to be certain, you are using YUM on a debian system or a guest? yum is a redhat/fedora package manager, the debian package manager is apt-get
my guess is that the system crashed in the middle of writing critical system files, leaving the system in a partially updated state with incompatible versions of software running, or only partially installed packages.
one way of fixing this is to boot a live cd, mount and chroot into the crashed install
(from a root prompt on the live cd)
# mkdir /rescue
# mount /dev/sda1 /rescue (or whatever your root partition is)
# mount --bind /proc /resuce/proc
# mount --bind /sys /resuce/sys
# mount --bind /dev /resuce/dev
# chroot /rescue
if it's a debian based system replace
# apt-get -f install
(you may have to install yum-utils package first for yum-complete-transaction)
i have had to do this more than once myself so i know it should work.