Thank you for your reply
I have an iMac 27inch, Late 2015, macOS Mojave v.10.14.4. 2GHz Intel Core i5 8GB,
After initial start up I have Google Chrome as default browser this is in order to check emails etc. I was then horrified to see a black screen, but when selecting another site ie Amazon it was normal as I would expect. An initial internet search provided numerous solutions all resulted with no success at all. I have just switched to Safari there isn't a black screen in Google. There is however two points that I would like to put forward. I have enabled Dark Mode and to my surprise when disabled to problem disappears. So there are to my mind these solutions, select Safari as default and disable dark mode by reverting to Light Mode.
My apologies for the scant details I was anxious to ask for some help.