that’s wherte i run into the problem- mine is oem- and only has 20 numbers in it- on the site you link to it must have 25 numbers- ie not an oem number
There should be a M$ number to call where they will certify online.
On the other hand,(I’ve never heard of this happening, but it is possible) they may tell you that your OEM is for 1 computer only (they may check the hardware for serial/ID numbers to see if they match). If that is the case, just let them know that you have changed the HDD (or some other peripheral (like a WiFi card, which I have done before)).
I’ve known of people that all they had to do was just to make the call (no questions asked) and were certified on the spot (and they actually had pirated versions). I have never had to do it myself (thankfully).
That made me curious, so I checked the one on my Toshiba laptop running W8.1, and it too is only 20 digits long. Ends with AAOEM.
Contact the manufacturer and see if they have a copy of Windows to download.
They may have their version with Windows plus all the ad ware.
Download the free product key finder:
ProduKey v1.97 - Recover lost Windows product key (CD-Key) and Office 2003/2007 product key.
http://www.nirsoft.net/utils/product_cd_key_viewer.html
Bigger article on the varoius ways to find your serial numbers:
How to Find Your Lost Windows or Office Product Keys
https://www.howtogeek.com/206329/how-to-find-your-lost-windows-or-office-product-keys/