I purchased a surface pro 3 years ago. I got a work image put on it 2 years ago. I wanted to replace it so, Microsoft gave me a download for a recovery USB (Windows V8.0). I want to upgrade now to 8.1 and eventually V10, but when I try to do so, it will not accept the product key in my registry (say that key won't work). Any idea what I need to do now?