content: Windows makes a fingerprint of your machine when you activate it the first time. If you do a clean install and try to activate it before all the proper drivers are installed, it doesn't look like the same computer due to the drivers not being there. I have worked in the tech field for going on 20 years now, it has been the same with every version of windows and licensing. Also if you change one piece of hardware, Eg: RAM HDD CPU it's not the same pc and you have to call Microsoft to get them to give you a new activation key.