Hi clarets2,
I'm making a few assumptions here but if you've downloaded and installed the iCloud for Windows app from the icloud.com website I'm thinking you should double check that there are no more updates available for Windows 7 on your computer. Microsoft does incremental updates, so it is important to keep checking for any updates until it says you're all upated or no more updates are available AFTER checking. In Windows 7, you should be using the Microsoft Update app. Learn more here: https://support.microsoft.com/en-us/help/949104/how-to-update-the-windows-update -agent-to-the-latest-version
https://support.microsoft.com/en-us/help/949104/how-to-update-the-windows-update -agent-to-the-latest-version
After you know Windows 7 is all updated; if you still cannot sign into the iCloud for Windows app, you might need to uninstall it and download another fresh copy. Instructions to uninstall are listed here:
Set up and use iCloud for Windows - Apple Support
Post again if you're trying to sign into something other than the iCloud for Windows app.
Cheers!
~Patrick