Yeah right. I now have my computer back from the doctors and it is now up and running again, although it has hiccupped once since, when I was trying to restart it. Fingers crossed that normal operating will be resumed.
The problem according to the technician was that ‘Windows’ had become corrupted. No known reason why, (and no other problems found, even under a stress test) although I know that the computer was doing a ‘Windows or Microsoft Update’ at the time. We will see what happens in the future.
Despite being out of warranty for 6 months, the problem was repaired under warranty. Thank you Samsung.