Many thanks Jock1e, as I had bought the laptop from John Lewis it occured to me that besides the 2 year warranty I also got a 90 day software support. So gave them a ring and a nice man called Dave told me how to reset to factory settings, as it was only a couple of days old and I had not loaded much on it (hold down shift key + press restart), worked fine. He also advised that once I had more data on the laptop a less drastic soloution would be a "refresh" to undo the last moves (PC settings-general-refresh), which was what you suggested in your second post. Now all set up and running fine, many thanks again.
iMac Pro review