If this only happens in one particular document, try clicking on
Tools | Unprotect Document. If all new and existing documents
are locked for editing, then it's probably because you have not
activated your Word/Office software, or because you have an
expired trial version of Office 2003. 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 purchase a key online.