Windows 7 should have come with a separate Product Key, the Vista Key is not applicable.  Also, doublecheck to make sure you are entering it correctly and haven't mistaken, for example the letter O for the number Zero.
-I had changed my hard disk after it was found to be corrupted.  Reinstalled win 7 and now the product key doesnt work. Any solutions? Who do i contact?
Windows 7 not accepting the key i had got with vista after free upgrade