grub repair

https://www.fosslinux.com/115031/troubleshoot-boot-problems-by-reinstalling-grub-on-linux.htm

boot with live media

sudo -i

mount /dev/sda3 /mnt
mount --bind /dev /mnt/dev
mount --bind /proc /mnt/proc
mount --bind /sys /mnt/sys

chroot /mnt
grub-install /dev/sda
update-grub

exit # ctrl+d
umount /mnt/dev
umount /mnt/proc
umount /mnt/sys
umount /mnt


Reboot without live media.

check the GRUB version by opening a terminal and running the following command:

grub-install --version