Faaaaaack that, google RemoveWAT.exe and you're good to go. All Windows operating systems (yes, that includes legit ones) ask you to re-activate and claim that your copy is no longer genuine once you add/remove a major piece of hardware. In some cases, it could even do it for something small like a Video Card or RAM.
In the even your copy is legit, you can just re-activate online or re-enter your key, or lastly if necessary, call in with your key and they will reactivate for you.
In the event your copy is NOT legit and it is downloaded, you need a new key, because you can't reactivate and must either do the crack (insanely easy) or re-install.