Malware can do things like this, so scan your system with your anti-virus, and also with malware scanners like Malwarebytes' Anti-malware and SUPERAnti-spyware.
The other option is, since you have that email or other document from Microsoft with the genuine details and code, give them a call on their free-toll number. It should be in one of those windows that is telling you your version is non-genuine.
Mark
I purchased a genuine copy of Microsoft office 2007, direct from Microsoft so I know that it is not a pirate copy, recently I keep getting a message coming up saying that my copy of office is not a genuine copy, and when I click on the more information I get told that my key has been misused, and has been used multiple times, but my copy has only ever been used once, I suspect that someone has used a keygen program and it must have generated my key, Is there any way that I can stop this message coming up as it does not look good to a customer, when he sees the message on the screen

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