iCloud pop-up to enter password and won't open on PC

I keep getting a pop up on my PC to enter my Apple password, which I do, then I get the ALLOW pop up on my Iphone, then the verification code. I put in the verification code, but then it just keeps returning to the password page. This just started after the last Windows update. It was suggested to update the ICloud app on my PC, but I can't seem to find that anywhere to update? It pops up dozens of times a day and is driving me crazy, not to mention my phone & calendar aren't syncing.

[Re-Titled by Moderator]