Problem now sorted.
Previously the laptop owner used a password (8 digit number/letter combination). For whatever reason this then failed. On the lock screen the invitation was for a pin number. Via the forgotten pin option, the route to change or insert a pin number was tried - this was blocked several times -so no success.
Laptop left for a few days, and tried again. This time, setting up a pin number was easy, and a four digit number pin was entered and at last success.
Still mysterious event for which I can offer no solution. (YES bastet, did check the number lock)
Thanks everyone for your comments, much appreciated
C