Hi there, I am John J.D., a fellow Microsoft user like you.
I'm sorry to hear about the activation issue you're facing. Let's troubleshoot this together.
What is the build number of Windows 10 that you are using?
You can find it by typing winver in the Start menu or the Run dialog box (Win + R key). Share screenshot in your next response.
How did you obtain your Windows 10 Pro product key? Did you buy it from Microsoft or an authorized retailer, or from a third-party seller?
Did you change any hardware components on your PC before or after upgrading from Windows 10 Home to Windows 10 Pro?
Did you try to activate Windows offline by disabling your network connection before entering your product key?
Looking forward hearing more from you. Let's work together to resolve the issue.
John J.D.