try a repair install, Windows 10 does allow that, when ask for a key say NO, it will still repair your installation, then wait about 3 min - move to settings, update/security. activation and see if not then you can chnag the key, when you enter your key that you paid for. (If it is not a pirate key) it should work. other wise you might need to use Digital Activation to convert to OEM and Activate.