When Debian based live ISO is booted start terminal and type:
mount -t proc proc /mnt/sda5/proc
mount -t sysfs sys /mnt/sda5/sys
mount -o bind /dev /mnt/sda5/dev
chroot /mnt/sda5 /bin/bash
Then run:
update-grub2
grub-install /dev/sda
When Debian based live ISO is booted start terminal and type:
mount -t proc proc /mnt/sda5/proc
mount -t sysfs sys /mnt/sda5/sys
mount -o bind /dev /mnt/sda5/dev
chroot /mnt/sda5 /bin/bash
Then run:
update-grub2
grub-install /dev/sda