I have just hardwired a second monitor to my laptop which runs Windows 10.
When I connect the HDMI the start page this happens:
1 very first page of my laptop is displayed
2. there are NO desktop icons displayed
2. my wireless mouse "switches" to the eternal monitor and the only way I can get it to work is to remove the hdmi connector so the functionality of my laptop screen is restored.
Very strange. I had no trouble using the same cable adpter for my wife's laptop and external monitor.
I have tried re-booting. I have tried switching the monitor off and then on.