I read up on a Microsoft site and there was a list of users in the USA and other places who had the same problem. They had connected a Windows 10 machine to an additional monitor and had resulted in black screen with cursor. Their solution was too complicated for me, loading a set up prog from another machine into a stick, connecting the stick to problem laptop, then when prob laptop starts up, break in and use stick. Or something like that with better terminology.
Thinking of going to PC world and paying £50