how did it break? Did it have to do with the recent GRUB update? If so, reinstall GRUB from the live USB. (do not use an old snapshot before doing that as it can break things). More info on the issue in this thread: Stuck in boot loop after update
If it has nothing to do with the GRUB update, you are going to have to fill us in on what is exactly wrong and what exact errors your are experiencing.