For the record, the issue was my SSD failing.

It is no longer detected, I have since installed o/s on a mechanical drive and it's all ok!

However I did have a bit of an added confusion - when I reset my bios defaults, the memory was giving errors during memtest68 - after testing 2 sticks at a time and seeing nothing was wrong - I realised it was the voltage had been reset in the bios! So I pumped it back up and it's stable again with memory.