Well I just tried to install windows 8.1 to my SSD and the product ID that I got from regedit seems to be 5 digits short of what I needed to install windows. For a while I had windows 8.1 and recently restored my computer and I think that put my computer back to windows 8 so maybe that has something to do with it? I don't understand why the product key would be different (if it is).
Edit: Even though I sort of mentioned this I would clarify and say my product key is 20 digits while the install key it asks for requires a 25 digit code.