If you start receiving Windows Activation Technologies warnings and errors, you need to know how to deal with the problem quickly to repair any loss of functionality. Windows 7 uses Windows Activation Technologies (formerly known as Windows Genuine Advantage) to hunt for pirates. Unfortunately, you don’t have to be a software pirate to run into problems with Window Activation Technologies (WAT).
If you’ve let your 30-day activation window elapse or if you’ve recently changed a lot of hardware, you’ll soon notice activation problems. Every hour or so the computer’s background changes to solid black and nags that “this copy of Windows is not genuine”. You’ll also see a balloon in the notification area of the taskbar telling you to "Activate Windows Now."
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To deal with a Windows Activation Technology failure, click the Activate Windows Now balloon. Windows will give you a message recommending that you contact Microsoft Customer Service to activate your copy of Windows.
Call the telephone activation number provided and talk to the representative. You’ll need to provide the original product key for your copy of Windows 7 and you’ll need to explain any hardware changes that you’ve made to your system.
They’ll tap a few keys on their end and you’re done. You’ll find that the folks in the activation department are aware that the WAT system sometimes catches good guys as well as the bad. Don’t be intimidated. The process is pretty quick and painless.
For more information, read Microsoft’s article about the Windows Activation Technologies.