This is just a reminder about the new login procedure for Office 2013 Pro. In order to use the new version of Office you have to login.
The first step, if you have never done so, is to login to Office 365 online here: https://login.microsoftonline.com
Use your email address and your network password as your credentials. You only have to do this once to activate your account (though feel free to make use of Office 365 if you want—you can download a full version of Office 2013 Pro Plus to 5 personal devices from here as well).
After that, if you encounter a login prompt when opening an Office product, login using your email address and your network password. It should only ask you once per computer if you have the ‘stay signed in’ box checked.