I have a laptop running Linux Mint and decided to give Ubuntu 17.10 a try. I wanted to go absolutely safe, so removed my HDD (actually an SSD, but shouldn't matter) and replaced it with a spare one (an older one that I was not using any more). I installed Ubuntu 17.10 on the spare drive and it works fine, but I would like to migrate to it later, since it's a longer process.
So for the time being I would like to go back to my old Linux Mint, which should be easy, since the original disk is intact. However, after swapping back the disks, I was utterly surprised to find that it does not boot up. The BIOS gives me a boot device selector menu, which contains four entries:
- [the model number of my drive]
- Linux Mint
None of which work (no error message, just returning to the same list). Booting up the live CD image from a USB disk I could confirm that my original disk works correctly. I can't fathom how installing Ubuntu could have made my original system unbootable when my system disk was physically removed from the laptop during the install process. I haven't modified any BIOS settings either.
My only guess is that it has to do with EFI/UEFI, which I have always considered black magic and don't really understand. I believe the OS names in the BIOS boot device selector come from UEFI and the fact that it lists Ubuntu suggests that installing Ubuntu may have had some effect on some BIOS state...?
Can someone explain this mystery to me and how I can fix it? Thanks!