You try to use a command on the ribbon, but the command is disabled or unavailable.
The trial period for using your Microsoft Office 2010 trial product, which is typically 30 days, has expired and the program is now in Reduced Functionality Mode. In Reduced Functionality Mode, you cannot create, save, or modify Microsoft Office documents. You can only view the documents.
Other possible causes are:
If you have been using a trial product that is now in Reduced Functionality Mode, to regain full functionality you must convert your trial product to a fully licensed version of the product. You do this by purchasing a Product Key online or from a retailer, and then by using that Product Key to activate the product. For more information on product activation, see Activate Microsoft Office programs.