Hi, Jacob,
Thanks for stopping by the Apple Support Communities. It sounds like you have changed your Apple ID prior to signing out of iCloud on your Windows PC, and now are unable to. We are happy to provide some information.
It sounds like perhaps you did not log out of iCloud before changing your Apple ID. If you haven't already you can try using the steps outlined in the Apple Support article:
What to do after you change your Apple ID or password
Open iCloud for Windows and click Sign Out.
- If you're signed out, sign in with your updated Apple ID and password. The data in iCloud will automatically appear on your device after you sign in.
- If you're signed in with your previous Apple ID:
- Click Sign Out. Depending on what iCloud options are turned on, you'll be asked if you want to make copies or delete iCloud data (Contacts, Calendar, Reminders, Bookmarks, Photo Stream) from your PC. Click Delete. Your data will remain in iCloud and will be updated on your device when you sign in to iCloud again.
- Sign in with your updated Apple ID and password."
See also this article if you are still having issues signing in:
Get help using iCloud for Windows - Apple Support.
Should you still need help after that, please reach out to Apple Support directly. You can do that here: Get Support.
Have a great day.