Grub Reinstallation

1.Boot with the installation media (CD/DVD)
2. Choose rescue existing system3. The system existing will be mounted on /mnt/sysimage

then, execute the following commands

#chroot /mnt/sysimage

and then

grub-install /dev/sda

assuming the your fedora system is installed on /dev/sda.

You can check this with fdisk - 

Once booted run:

chroot /mnt/sysimage

/sbin/grub-install /dev/had

chroot /mnt/sysimage

grub-install /dev/sda

exit