Please remember that pop-ups telling you that you need to do something (whether that be updating Java, updating Adobe Flash Player or, your case, getting a genuine version of Windows) are often FAKES which are generated by malware on your computer. (Clicking on them will either do something really nasty, like installing Cryptolocker on your computer, or else demand payment for a 'fix' which you don't need).
Please run a malware scan with the free version of Malwarebytes Anti-Malware:
https://www.malwarebytes.org/antimalware/