Hi Saurabh A, thank you for replying. I have followed the instructions in your first paragraph. System restore worked right through to the end, leaving a message, which I have attached.
I then followed the instructions in the last paragraph, and the diagnostics reported all OK.
I then rebooted into 'normal' set up, and the system restore message was there saying it had not completed successfully, so I started it again. Sadly, the same problem persists where by it 'hangs' on initializing.