That makes sense, because you have what's referred to as a KMS Product key, which can only be activated when you are connected to the Educational Server it belongs to.
Basically you have an illegal copy of Microsoft Office installed.
My advice, either purchase legal product key [ and if you do that, buy a more a current version of Office, not a 2013 one ], or uninstall the software and install one of the free options others have suggested.
That begs the question as to whether your Windows Operating System is also an Educational copy that belongs to the University or College who paid for the licence.
I believe this thread now needs to end, so I'll be locking it from further input.
I wont delete the thread, as it serves as a timely reminder to people that they need to be careful whom they purchase a computer from, because of the number of thieves out there who can leave people like yourself in a real jam.