My thanks to those who replied to my post and suggested several ways to
solve the problem.
It has now been resolved and I thought others may be interested to learn
how.
While talking with a visitor, who is quite computer literate, he suggested
that we look at what was loading at Startup.
I have WINPATROL installed and we used this to disable the Startup items
one-by-one, then tested "Shutdown" each time.
The culprit turned up to be the exe. file for SOLITAIRE, which I certainly
had never set to run!
Who knows, computers are funny beasts, but no matter things are back to
normal again so all is well.

Here's hoping someone else may be able to make use of this info. if they are
in a similar situation to mine!