Black filling of cells when merging

Hi there,

I've joined the forum mainly because I have no idea what to do with this problem!

Am a long-time Excel user but this has only happened fairly recently. We've had Windows 10 since early this year. I've done a lot of work since then and this problem has only emerged in recent weeks.

Problem: When I select some cells to merge, the rest of the cells become black - all rows and columns except the selected cells. (Have a screenshot if necessary to send to you)

Escape by using back arrow.

I'm pedantic with layout, so not being able to merge/centre cells is very frustrating.

Thanks!

Thank you for your prompt reply.
This does seem to be quite intermittent, which makes me scratch my head even more.
When it does present, I can't merge the cells unless I "back arrow" and repeat the process. It doesn't keep the merge initially, but eventually it seems to work.
However, I've just discovered a trick that works every time!!
1. Select cells to merge - whole page except "cells to merge" fill in black. 2. Go to cell A1 and click on it. VOILA!! Black disappears and cells are merged.
Usually I'd like to know why/what I've done, but I'll just accept this works and get on with the job!
Thanks for your input!