On a windows 10 computer, sometimes you have an HDMI port and a VGA port. Normally, you only have 1 monitor. When you try to plug both ports together, windows guesses you have 2 monitors so when you scroll to the right, the mouse disappears.
Now if you remove the VGA cable you will see a black screen. The secret is the Windows+P key. When you press this button, the system automatically switches to HDMI port. Please note that this step would take around 10 seconds to kick-in.
At first I thought it did not work. But patience is truly a virtue.
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