Assuming the following situation, you did something and you also smeared your MBR record. And then you don't have or just get an error message in GRUB. Recovery is a trivial operation from anywhere

1. Make whatever Live CD / DVD / USB you have on hand with any distro

2. Switching to chroot on the start of your OS will save your settings and use the version of grub with which they were with me and I have a lot of things described in the CMD of Grub

mount /dev/sda1 /mnt
mount --bind /dev /mnt/dev
mount --bind /proc /mnt/proc
mount --bind /sys /mnt/sys
chroot /mnt

3. We have already chroot your distro left only to reinstall rough and update (just in case)

grub-install /dev/sda
update-grub

Воала рестартираме и сме готови да работи както преди и всичко е непокътнато ни лук яли ни лук мирисали 😉 Възстановяване на GRUB