If you have a problem that caused your grub to be deleted, and if you have a liveCD or the kind,
open a console window and
sudo apt-get install lilo sudo lilo -M /dev/sda mbr
In my case, I was trying to format my partition and install a version of linux mint. My usb disk had a faulty part, so, it gave an error halfway and I needed to restart in order to create another bootable usb disk. I couldn’t… Because now I didn’t have the bootloader to select OS.
I reopened my faulty usb disk’s on-the-fly OS, opened a console window and run these commands.
I’ve got an error in the install part, though… but it didn’t matter at the end, since I could run second command successfully.
With lots of love.
Have a nice weekend.