In case something is f****d up with multiple partitions, multiple grubs etc.
1)Live Ubuntu CD startup
2)sudo fdisk -l
to check the right sda (in my case sda2)
3)sudo mount /dev/sda2 /mnt
sudo mount /dev/sda2 /mnt/boot
sudo mount --bind /dev /mnt/dev
sudo chroot /mnt
grub-install /dev/sda
4) Cntrl+D
5)sudo umount /mnt/dev
sudo umount /mnt