Need To Reactivate Your Product - Cant Use Microsoft Word

Before a couple of weeks, word and all the rest was working perfectly well but since recently i cannot use it anymore.

When i open Word, an error message comes up with: Microsoft XP professional has detected an important modification in the configuration of your computer. To be able to keep on using microsoft office xp, you need to reactivate your product.
To start the reactivation process, pleas insert your microsoft xp professionnal CD