Gary
Thanks for the suggestion.
Norton Everything was indeed running in the background, and I have now disbabled it, but sadly with no real improvement.
It's only a minor fault, every now and then, hard to see on a small screen but impossible to miss on a large one.
I am now trying to see what else may be running without me being aware of it, failing that, I'll try reloading everything.
Many thanks
Bellerophon