Windows Not Genuine, even though Copy is Purchased

Hello, Since yesterday morning I've been getting the message "Windows 7 Build 7601 This Copy of Windows is Not Genuine" on my HP Pavilion Elite desktop computer, which I purchased in 2012. I called Microsoft and they said that HP was blocking my copy. I then called HP, and they said they don't do that. I then explained to HP what happened. They thought it might be a virus that was the...