Most people are moving to Office 365, which is a cloud-based subscription product. The activation key is tied to your email account, and you must renew the subscription according to your plan.

The "Product Activation Failed" error in Microsoft Office arises when the application cannot verify your license or ...

Office 2010 will now use Key Management Service (KMS) to activate your product, further simplifying the installation process of Office 2010. KMS eliminates the need to manually enter license codes ...

Unlike the retail versions of Office 2007, copies installed using volume license keys -- the typical way large organizations purchase Microsoft's software -- will simply skip product activation ...