Thanks for the response. Before I could attempt any of that, the message has disappeared by itself. I wonder if Windows is in the background constantly contacting a Microsoft server to "verify" its genuineness, and there was a problem with the server? In any case the message is gone now.
I purchased the Windows disks from a reputable seller, along with the hardware for a system I was building, so as far as I new it was a genuine version. I contacted the seller, and they were quite surprised, and suggested similar actions as you.