Boot from Live CD / USB

open a terminal

sudo su

mount your linux partition (in my case /dev/sda5)

mount /dev/sda5 /mnt

mount specials

mount –bind /dev /mnt/dev

mount –bind /proc /mnt/proc

mount –bind /sys /mnt/sys

chroot to your mounted linux partition

chroot /mnt

update ad install grub

update-grub

exit from chrooted partition

exit

unmount all

umount /mnt/sys

umount /mnt/proc

umount /mnt/dev

umount /mnt

reboot