Igor,
You are a star :) Thank you so much.
I saw Nvidia mentioned in a couple of places when I was investigating this problem but had no idea what Nvidia was. I inherited the laptop and it is an MSI gaming laptop. I've tried to create a login 3 times via the App on my laptop but encountered an error each time. I crossed my fingers for luck and deleted the Nvidia App and, hey presto, everything appears to be working properly again.
I have looked online and found Nvidia but have not downloaded anything from them because I'm not sure if I need the App now. I don't use the laptop for gaming and that seems to be Nvidia's purpose.
Thank you again. Great advice.