I installed Artix to see how it works and after uninstall this system the grub was gone ...
I tried to get the grub back by installing the Manjaro i have in a USB, with this command:
# grub-mkconfig -o /boot/grub.cfg
(from the terminal of the system in which i want to have the new grub).
-- then, after this, i go to gparted and remove the Manjaro/USB from the partition, but after reboot ... the grub is gone.
I don't know what is wrong, how can i recover the Grub now?.