My 14in colour monitor displays a split screen with the same information on both sides. It does this on all the computers I connect it to. It didn’t used to. How do I fix it?

You can assume that it is a hardware problem with the monitor because it has a split screen on all the computers you connect it to. Since it is a hardware problem there is not much you can do to fix this problem. I suggest that you take the monitor into an electronics repairer and ask them to take a look at it for you. NB: DO NOT try and fix it yourself. There are very high voltages inside the monitor and attempting to fix it yourself could result in physical harm. There are also no user-serviceable parts inside the monitor. Only a qualified repairer can replace them.