Okay, seriously, this sounds like its malware of one sort or another.
Find this screen, by clicking on your start menu, then right clicking on "Computer," and selecting "Properties." Does it look substantially similar to the screen that I've shown here? If it does, then you've got some sort of malware that's telling you that you've got an invalid copy of Windows for the purpose of getting you to give them a credit card number or some such.
On the other hand, if you don't
have something that looks substantially similar to what I've shown here, then there's some sort of issue.
Which is it? I suspect that it's more likely the former than the latter ...