Apparently, the computer manufacturer installed a trial version of Microsoft Office on your new computer. You'll need to purchase a genuine perpetual license for Microsoft Office in order to continue the use of the program.
The product key affixed to your computer is only for Microsoft Windows, the operating system, and not Microsoft Office.
How to convert a trial version of a 2007 Office suite or program to a full retail perpetual license version:
http://support.microsoft.com/kb/927756/en-us
How to determine whether you have a trial edition of a 2007 Office suite or program installed:
http://support.microsoft.com/kb/927920/en-us