After quitting Rigo and rebooting the system the GRUB menu now displayed only two options:
Advanced options for Sabayon GNU/Linux
Selecting the Advanced option displays the menu of kernels, which is the normal menu I would usually see. Selecting any option from the GRUB boot menu first results in the message:
error: file not found
repeated three times followed by various normal bootup messages until the last message stating:
!! Could not find the root block device in .
and the prompt:
root block device() ::
I tried /dev/sda4, which I would expect it to be, but without success. /boot is on its own separate partition but the rest of the system is on logical volumes on an encrypted partition, sda4, so I would normally expect to see a request for the passphrase at this point. If I boot from a live installation media I can manually enable the encrypted partition and mount the logical volumes and see the files on them.
I am not sure how to proceed to identify and fix the problem so the system can be fully booted, could someone advise please?