iCloud log in prompt keeps coming up on my Windows laptop - with an old email address

Every few minutes, a log in prompt keeps coming up on my laptop. The user name is a previous email address. It won't register a previous password or my current one for this old email (just to enter to get rid of the prompt)

When I log into iCloud using my current credentials - I can access account no problem. I've checked the emails stored in my account, and there is only one that I can see, my current one.

Very confusing - as when this prompt comes up, a window pops up behind it with my current and correct account info - so a different email address (the correct email address).

Hope this all makes sense? Anyone know how to fix this?