Welcome to Justanswer.com, my name is ***** ***** I will do my best to assist you.
The info Issac gave you was correct.. What dell told you was incorrect.
Regardless of whether your computer is window s10 compatible or not.. The issue is the product key
If windows 7 says its validated and genuine.. Then when you upgrade to windows 10 now then windows 10 will also be genuine.
The problem before was, when you replacede the hard drive something must not have been entered correctly for your windows 7 product key.. So when you upgraded, it couldnt validate.
Keep in mind that if you have a working copy of windows 7 or 8.. windows 10 is free.. So if your current windows 7 is now genuine, then windows 10 will be genuine if you update.
I strive to provide great service, and greatly appreciate a 5 star rating clicked and submitted when you are satisfied.. I always answer follow up questions.
Senior Technician and Network Switching Systems Operator / Maintainer.