If you bought the box product at a store and you haven't installed Office 2016 yet, the product key can be found in the packaging.
If you continue to have problems signing in to your account page, contact Microsoft support to review your options. If you sign in to your account page with a Microsoft account that's not linked to your subscription, you'll get this message: ' Office isn't associated with this account.' You'll need to sign in with the Microsoft account that was used when you redeemed and installed Office for the first time.
