Thanks for the responses and sorry for not responding earlier, Explorer decided to collapse again as I was trying to respond!
I checked and found that the system had created a system restore point just before this morning's update so I tried to restore to that. I got a message saying the restore failed but no information as to why. I tried again, failed again. I then tried to restore to an earlier point - same thing happened.
I have an Acer Aspire E1-572 which is only a few weeks old. I think one thing that could be complicating matters is that after the problem started, I uninstalled Avira and replaced it with BitDefender, so I assume the Restore is trying to reinstate Avira and can't find the files?
I know it was probably dumb to do that, but what started the trouble this morning was that when I went to do my Windows update, I noticed that Avira wasn't auto-updating and after Googling it, found that it's a problem with Avira and Windows Firewall. So I wondered if Avira might be causing some of the problems.
I uninstalled BitDefender in case it was blocking the Restore and tried again, but it still fails.
No discs were supplied with the laptop. Since getting the laptop I've been working mainly on the cloud so there isn't much in the way of files that I'm worried about.
Edited by Marisawriter, 27 June 2015 - 04:37 PM.