How to restore Grub after installing a new kernel (or Windows)

To reinstall my working grub, i've read and applied the steps mentioned in this tutorial. It worked like charm!

Using Ubuntu 9.10 livecd or higher
Here assuming the Ubuntu partition is sda7,and /boot partition is sda6 (if you have a separate /boot partition).
Boot up ubuntu from the livecd,open terminal and run:

sudo -i
mount /dev/sda7 /mnt
mount /dev/sda6 /mnt/boot  #skip this one if not have a separate /boot partition
grub-install --root-directory=/mnt/ /dev/sda

If you miss “grub.cfg” file,use following to recreate:

mount --bind /proc /mnt/proc
mount --bind /dev /mnt/dev
mount --bind /sys /mnt/sys
chroot /mnt update-grub
umount /mnt/sys
umount /mnt/dev
umount /mnt/proc
exit