Sometimes a Microsoft product key shown in Belarc software doesn't match the key on the Microsoft sticker, or only shows a few characters of the key. One common cause of this is that the software was pre-installed by the computer manufacturer and your personal product key was sent on a separate card or sticker. Computer manufacturers often use their product key, instead of yours, when pre-installing software at the factory so that's the key you're seeing.
Another common cause is that recent Office installers remove all but the last five characters of the install product key once the installation completes.
To change the product key currently on your computer (and reported by Belarc) to your full personal key, you can follow the steps outlined below.
You can change your Windows product key by following the instructions at this Activate Windows Microsoft web page, in the Activate Using a Product Key section. Those instructions work on many versions of Windows.
Purchasers of Office 2013 and later usually receive only a Product Key Card and instructions to download office from the office.com web site. The 25 character key on that Product Key Card is not your office install key, but instead an entitlement key allowing you to install office from that web site.
You can see the product key that is used to install office by signing into your office.com account here. Once signed in, just click the View product key link under your edition of Office and you'll see your office product key.
You can change your Office 2010 and 2013 Professional Plus or later product key like this
Note: You must have an internet connection to reactivate Office online. However, you can also activate Office at a later time by opening any Office app, clicking on the File tab, and selecting Help.
You can change your Office 2007 (or older version) product key by following the instructions at the How to change the product key for Office XP, for Office 2003, and for the 2007 Office system Microsoft web page.