If you MBR ( Master Boot Record ) is corrpted , you are unable to boot into Linux. Then you have to restore the GRUB boot loader.
To do this, you need a linux distribution CD. If you are using Redhat , fedora CD version then you only need first CD . But you may also use any af the live CD's like Ubuntu , Redhat and so on.
Then you boot your PC using first CD of Fedora, and enter the following command at the installation boot prompt
( installation boot prompt == after booting cd , first stop window)
boot: linux rescue
.... Press enter , after press enter you have to select " language , type of keyboard ,
how to boot like network boot or not"
# chroot /mnt/sysimage
# grub-install /dev/hda
NOTE : If you have an IDE harddisk "/dev/hda" ,
If you have a SCSI harddisk (Sata) "/dev/sda".
# exit
# reboot
Now you can boot your Linux OS...............