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"I see messages that Windows might not be genuine. How do I fix this?
If you're seeing notifications that the copy of Windows that is installed on your PC might not be genuine, or that you might be a victim of counterfeit software, it's likely that your copy of Windows was not properly activated or is otherwise not genuine. To fix this, click the notification and follow the steps to either repair Windows or—if you have inadvertently obtained counterfeit software—buy genuine Windows.
Until you correct the issue, you'll receive periodic reminders that Windows is not genuine. In addition, to more clearly display these messages, your desktop might turn black. You can reset it, but every 60 minutes, it will return to black until the issue is resolved.
Regardless of genuine status, Windows will still be able to get critical security updates. However, access to optional updates or benefits available exclusively to genuine Windows customers, such as Microsoft Security Essentials, might be restricted."