I have seen the 'this copy of windows is a fake'or whatever it says twice and I bought mine from Amazon. Try this.
You can use WAT (Windows Activation Technologies) to confirm if copy of Windows 7 installed on PC is genuine or not. WAT also help protect against the risks of counterfeit software. It is an online check that enables you to verify that the copy of Windows 7 that is running on your computer is activated correctly and is genuine.