This has happened twice before. For no reason at all that I can fathom I log on and find that I have broad black margins at the side of the screen.
On those other occasions I was receiving helpful advice while messing about with the full screen icon and, before I could follow any of the advice, it returned to normal.
So I never did find out what caused it or what cured it.
It’s happened again, but messing about, including rebooting, has not helped. I followed some instructions which brought me to a Resolution box and was advised to choose 1920-1080 from the drop down menu.
The box says I have 1024-768, but it is greyed out so I can’t change it.
Any suggestions please? A laptop screen is small enough as it is without making it even smaller.