Thanks everyone.
I had re-installed Service Pack 2 and could not see any key icon on the screen.
After spiralling into more and more expletive use, I bit the bullet and telephoned Microsoft Helpdesk. I was talked though numerous changes to .dll files
and eventually all seems sorted.
I have written out a hundred times 'I will leave my computer alone' in the hope that I have learnt my lesson.
Very many thanks for your suggestions of help.
Kind regards,
Brian