This could be a false warning from a virus, as well. Please run through the following steps so that we can confirm it is activated correctly...:
MGA Diagnostic Report:
To properly analyze and solve problems with Activation and Validation, we need to see a full copy of the diagnostic report produced by the MGADiag tool (download and save to desktop - http://go.microsoft.com/fwlink/?linkid=52012
Once downloaded, run the tool.
Click on the Continue button, after a short time, the Continue button will change to a Copy button.
Click on the Copy button in the tool (ignore any error messages at this point), and then paste (using either r-click/Paste, or Ctrl+V ) into your post.