Why are you posting this again in another subforum?
Go into the User Control panel and create a new user.
Reboot the computer (assuming that you still can after the attempt to reload Windoze) and log in as the new user.
Also, I seriously doubt that mp3car.com store is going to sell you a copy of Windoze without the CoA & corresponding key. Is there a Windoze CoA sticker anywhere on the case? That's where OEMs are supposed to put the CoA sticker, anyway....