This is what you do
Reboot with the first fedora cd and it should take you to a cml
type
# linux rescue
Basically the first cd is a rescue cd that looks for you linux partiton and mounts it on
/mnt/sysimage
After a couple of questions asked, hit enter on continue to mount the linux partition if it is detected.
When it drops you to a cml - type
# chroot /mnt/sysimage
Then try to reinstall grub on your mbr by typing
# /sbin/grub-install /dev/hda* hda* is you root device "/"
After that reboot with the cd out and give it a try.
Hope this helps