For one reason or another, mainly due to motherboard and/or CPU replacement, I've had to reinstall Windows 10 numerous times on my two main PCs, resulting in having to reactivate Office 2013.
This can be a challenge if Office has already been activated on another PC previously and the process for deactivating Office on a hard drive that you will no longer use, can also be a tad troublesome. Also, if you've already formatted the drive, you clearly can't uninstall Office from that drive, thus deactivating it.
However, you can activate your legal copy over the phone, but due to a bug, telephone activation is often not available.
I found a Microsoft page which shows the correct toll free numbers in order to get around this error, thus allowing you to activate Office.
Telephone activation is no longer supported for your product" error when activating Office
Simply input your country and the correct number will show up, then start the activation wizard in Office, which should look something like this:
Choose telephone activation, click next and the following window should appear.
Call the phone number and an automated service will prompt you to input the numbers in the nine blocks above, following which you'll then input a series of numbers which will be read out to you, into the eight sections A to H.
At the outset, I was asked to input how many PCs this copy of the software had been activated on and I input 1.
Having done that, click next and your copy of Office should be activated.
This process is perfectly legal and above board.
