Thank you all for your replies
As the previous install of v5.27 can’t boot from the hard drive, I can’t SSH into it.
So to update, I’ve tried every combination of flashing v34 and v5.27 from different USB sticks, and using Rufus to flash instead of Etcher, and waiting up to 4 hours for the USB drive to boot, but it’s all just a black screen and nothing loads.
Also I’ve even tried booting from USB an image of Windows (8.1) which is known to work, and it doesn’t load either.
Anything idea how the boot install could be so hard to achieve?