If you receive error "0xC004C008" when trying to use Windows 7 online activation, it could be for one of the following reasons:
Your computer’s hardware has been changed.
Windows 7 was reinstalled on the same computer.
Your Windows 7 product key was transferred from another computer.
The Windows 7 product key that you’re trying to use has already been used on the maximum number of computers that your license allows.
If you changed your hardware, reinstalled Windows 7, or transferred your product key, you’ll need to activate Windows 7 using the automated telephone system.