I had the same problem, the exact same problem.
what you need to do is enable yum updates via http://rpm.livna.org/
(read how to do that on the site)
then run the command "yum udate" (as root), it'll download the newest kernel and the newest drivers.
My problem was that I had a nvidia graphics card that FC5 misinterpeted. I needed to do the following as well:
"yum list *nvidia*"
"yum install everything that had to do with nvidia drivers"
now everything should work, except one thing that still bugs me:
The boot up screen (the nice graphical one before the login screen) is still messed up. You can go around this problem by editing the GRUB boot loader config /etc/grub.conf and removing the "rhgb" command. This will keep the boot up plain and simple (with just big green "OK"s).
Even if you don't have a problem with the graphics card but with the monitor or something else the newer distros (that you install with yum), will detect much more hardware correctly.
I hope it works,