Maybe you have a trial version of Office 2003 or 2007, and the trial
period has ended.  Or maybe you have not activated your Office software.

What happens if you start Word and click on Help | Activate Product?  If
you are already activated, a dialog box saying so will appear.  If you
are not activated, the Activation Wizard will start.  If you have an
expired trial version, a dialog box will prompt you to enter a valid
product key or convert (purchase a key) online.