The issue you're describing is very much what happens when there is a Pre-Activated version of Windows 7 installed on a machine which has been updated using KB971033
or possible even the new SP1 release.
With a Pre-Activated version of Windows 7 there have been changes to the activation files to prevent Windows from requiring activation and the above KB
restores those files to how they should be. There are pirate versions available which have had this technology tampered with. I'd suggest following Brink
's excellent advice in making sure that your copy of Windows 7 is genuine.
Please not we do not promote piracy here on sevenforums