Thank you for your help and support, I have solved the problem. I DO know what happened, but I do NOT know how it happened. I am utilising a second monitor, which is only switched on when needed, that is when I am working in an app which requires reference to other files, which I then place on monitor 2. I did NOT use this facility when the problem first occurred, and it was only by chance that monitor 2 was switched on and all was revealed. When Word was shut down from this monitor and I returned to monitor 1 everything functioned as normal. I am grateful for the input that I received, and only hope that one day I may be able to contribute to solve another members problems