From http://www.cyberciti.biz/tips/howto-fix-dual-boot-windows-vista-linux.html
Step # 1: Boot from Fedora Core Linux 1st CD or DVD
Set BIOS to boot from CD/DVD rom. At boot: prompt type command linux rescueboot: linux rescue
Just follow on screen instructions, when prompted let installer search Linux installation. If the search operation is successful, your old Linux installation will be available at special directory called /mnt/sysimage.
Step # 2: Prepare system for GRUB reinstallation
Type the following commands at shell prompt:# chroot /mnt/sysimage
# cd /boot/grub
chroot command allows to run rest of all *COMMAND* with root directory set to NEWROOT called /mnt/sysimage. Without chroot environment you will not able to restore GRUB on Fedora Core 6.
Step # 3: Find out your GRUB bootloader installation location
If you have only one IDE hard disk default should be /dev/hda. You can use any of the following command to determine your device name:# grep '#boot' grub.confOuput:
#boot=/dev/sda
Above output clearly point out that /dev/sda device where my GRUB bootloader was previously installed.
You can also try out fdisk -l command to list partitions and disk information:# fdisk -l
Step # 4: Reinstall GRUB
Use grub-install command to install GRUB on your drive /dev/sda# grub-install /dev/sda
Please note that if above command returned any error return with –recheck option to probe a device map even if it already exists# grub-install --recheck /dev/sda
Step # 5: Reboot system
Exit from chrooted enviorment and reboot Linux:# sync;sync;exit;exit
# reboot
