For anyone who comes here in the future.
It turns out I didn't need the "DDU" tool that the person below advised, which was lucky as it looked to be pretty complex and would have required quite a lot of work to understand it from a lay computer user like myself. They were right about my Graphics-Card Driver being the issue though; but the problem was that that Driver was very much out-of-date; this was because this particular Driver had slipped past, undetected, the Dell and Windows Driver-apps I mentioned in my comments of this thread, and so had not been getting updates along with the other Drivers on my PC.
I installed the "Intel Driver & Support Assistant" app which was able to track my Graphics-Card Driver, my Graphics-Card having been made by Intel. This app was then able to update my Graphics-Card Driver which solved the problem. This Intel app also spotted a couple of other Drivers in my PC which had likewise been undetected by the Dell and Windows apps, the Bluetooth Driver and a Wi-Fi Driver.
I know that people often search through old posts on here for help with problems, which is why I feel it important to make this note.