Still a good idea to backup /home.
Do you have 10 to 25GB available on drive? You might just want to put a new install into a new / (root) partition so you can do more than just test drive with the live version.
You should be able to chroot into your install and run repairs.
But if just a booting issue this may help.
Post the link to the BootInfo report that this creates. Is part of Boot-Repair:
Boot Repair -Also handles LVM, GPT, separate /boot and UEFI dual boot.:
You can repair many boot issues with this or 'Create BootInfo' report (Other Options) & post the link it creates, so we can see your exact configuration and diagnose advanced problems.
Install in Ubuntu liveCD or USB or Full RepairCD with Boot-Repair (for newer computers)