Use your FC2 installation cd to boot (just like when you installed and look for 'rescue' instructions in the boot screen.
Once you're inside your system, you'll have to chroot (change root) to the partition your original root was on (e.g. /dev/hda3) and just to make sure the right /boot partition is mounted you might want to
$ umount /boot
$ mount -a /boot
then reinstall grub with
$ grub-install /dev/hda