Reinstalling GRUB2 (Manjaro)

Load up a live distro of Manjaro. Determine the partition where Manjaro is installed. (Example /dev/sda2).

blkid

Mount the partition:

mount /dev/sda5 /mnt

Mount the swap:

swapon -a

Change the root directory:

arch-chroot /mnt

Install mtools and os-prober:

pacman -S mtools os-prober

Install grub to /dev/sda. (Because Manjaro on /dev/sda5. Or you can select different HDCode):

grub-install /dev/sda grub-install --recheck /dev/sda

Configure new grub.cfg file:

grub-mkconfig -o /boot/grub/grub.cfg

Press Ctrl+D or:

exit

Reboot:

reboot