After a long period using Hibernate from Elyssa, I decided that it is time to do a re-start. Now this always fails and lands me in Busybox. Various Wiki articles give some guidance, but I've found none referring to the Debian version built into Linux Mint.
In principle it should be possible to boot from Busybox - but how? In it, I can cd to /root which turns out to be my defunct Windows system - I can navigate to any file in that via cd.
But if I cd to /dev, ls -a shows its contents, including sdb2 where Elyssa's root folder is installed, but it reports "Can't cd to sdb2".
Currently Supergrub fails to boot me into Elyssa. At present it's giving me a long-lasting black screen after Enter to select Elyssa for booting.
I'm sending this under Windows from my laptop - and still hoping for advice about my failed installation of Elyssa on an external hdd which was connected to this. I had to use Supergrub to restore the Windows MBR on this machine after that attempt.
Addition by edit: I've used Supergrub to fix the Grub Bootloader in the PC Elyssa installation: it still goes to Busybox every time. When I first installed Elyssa, it used to go to Busybox 2 or 3 times, then boot properly.