Activating Microsoft Office 2013 with a new serial key

I had a lot of trouble activating Office 2013 Professional because the activation key I used during installation was invalid. After installation, it would ask me to activate it again. But the activation window would never allow me to enter a new serial key. It would use the same serial key I used during installation and obviously complain that it was invalid.

The workaround for this is (without having to activate over the phone) is to use command prompt. So much for Windows being a GUI OS.

Run command prompt and enter the following commands:
(The path should match to your installation directory on Windows)

cd C:\Program Files (x86)\Microsoft Office\Office15\
cscript ospp.vbs /inpkey:YourKeyHere
cscript ospp.vbs /act


The second command replaces the serial key on file with the new one you enter. The third command activates it with this new serial key.