Problems with product key

Welcome

The obvious answer is that it is invalid, but we will assume that not to be the case. You can call this number, and use a touchtone phone to input the number. If that does not work you will be elevated to a rep. You can explain the situation and he will activate you. This is the only course of action.
http://www.microsoft.com/licensing/e...n-centers.aspx

I will also give you, what should be a prize winning, a copy of an applicable tut.

Activate Windows 7 by Phone

You will not have a problem. These reps are really helpful, courteous and professional.