Man thanks for contacting me. Problem was caused by faulty mouse so now sorted.

@dan-mitchell Hi Dan
TY so much for your advice. Altho the white screen is most irritating on Lex, it is my home screen that is also white & nothing to do with Lex. I def think it is connected with the latest Windows 10 updates. I am going to wait for my son-in-law to visit in the hope that he will be able to fix it for me.
Elaine

@ray-schreffler I have the answer!! In your Windows settings, disable high contrast & it goes back to normal. Elaine xx