what did you update with YUM ?
idont know why, but fedora acts very badly when you update runnng programs....
for example if yum updates KDE (kwin) while it was running it causes problems, like old shared libraries that should have been deleted hanging aaround and such..... Other distro's like Gentoo handdle this fine.... but not fedora.
its probably not the same problem.... but if it is, there is how i fixed it....
login as root and kill the x server (dropping to runlevel 3)
nor forcably uninstall KDE.... this will break some dependency's, but they will be fixed next.
//searhc for kde packages installed
rpm -qa | grep kde
// making sure ONLY kde packages turned up in the search forcably remove them
rpm -e `rpm -qa | grep kde` --nodeps
// if the search returned packages yyou dont want uninstalled, then you will have to rpm -e packagename by hand.
then re-install the kde packages forcably.
rpm -F kde*.rpm --nodeps
remember..ONLY truy this if your system was damaged in a similar way to mine...