Strange Desktop

Hello, if this is the wrong forum please direct me to the correct one.
I'm running W10 on a Lenovo 2-14 Flex.
My desktop which has always been a slideshow has suddenly gone into a black and white block pattern as shown in the picture.
I've checked the setup and customisation of the desktop and it is set for slideshow.
The icons are responsive and other pages such as Chrome or videos etc all appear normal.
Can anyone help please?

 

Looks like you might have a very high resolution pic selected as background, and you have the "chose a fit" setting, set to center, or maybe span? change it to fit and see if makes a difference. It kinda looks like a giant direct x pic. Also try changing the background setting from slide, to picture, and then back to slide. Sometimes it will get stuck for some reason.

 

Thanks for the reply.
When I first got up I get my normal background picture but once I sign in it changes to this.
In display the resolution is set to recommended 1920 x 1080.
In personalise I have changed from slide show to picture. It was set on fill. I have set it to fill.
IT WORKED!
I have reset it to slideshow again but it doesn't seem to be changing. Never mind though I can live with that. Thanks so much for your help. Jan