I have tried that, holding the reset button for at least five seconds. It made no difference.
I'ts after 1am here and I have to get some sleep. I will take a look in the morning (in six hours or so) to see if you have any other suggestions for me to try.Thanks for your help.
I'm afraid I didn't get a chance to do it Thursday morning as I was racing for a train and I won't be back home again until Monday. I had to get the urgent print job done at a professional print shop. I will try unplugging the machine when I'm back in London.