Thanks Saab and Irish. The link Irish gave is the problem. I tried to save a word document after I started this thread and the the computer froze. I've also noticed that my computer is very slow to wind up when I switched it on, anybody else noticed this? This slowness may have started when I recently installed a HP 8050 printer (to replace a HP940) I wonder if it is associated with the faulty update.
This forum is great, you computer geniuses have helped again!