After letting the OS re-install? I ran the disk utility. Only the First Aid and Partition options were not greyed out. Erase was not enabled. First aid ran a test and said drive OK.....
Machine still didn't boot up to a desktop. Apple Icon didn't do anything.
I removed the drive from the machine, popped it into a disk caddy and fully erased it, removing the partitions as it went.
Job done, no personal data left to fall into the wrong hands.
Thanks for guidance and prompting.
Rans6.............
ps, if I load Linux Mint onto the drive and refit it - is there any chance that it will boot up? I might try that tomorrow.