Cant activate after hardware change

BUT, the database Servers of Microsoft see what you did/changed as a new computer and the Product Key/s you have doesn't match their record as being available, has already been used. It probably will take a phone call to make it work. There usually is a prompt onscreen with a longish code to be entered to get back a code to enter. If that doesn't work there should be a phone number to call.

Also possibly involved is whether an OEM or Retail version key was used, the OEM or System Builder version is licensed to one computer and only on the hardware it is first installed while the Retail version can be moved to a replacement computer, used to be only once but have heard that has changed.

Raigan said:

I upgraded my system with a new mobo, ram, cpu, SSD etc.

Possibly too much change for previous key to be accepted, if ...

I retrieved my Windows 10 Home CD Key from a Keychecker app i downloaded on my old machine, installed windows 10 on my new machine using windows 10 installation media.

Was this key an OEM key ?

Also, possibly false license reading from key checking app (common problem). Did you install Windows in the first place ? Is there a license sticker on the device ?

Do you have the old OS still installed on a drive (already activated Windows is very forgiving when hardware is changed; you may be able to re-boot with the old drive and recheck the license with ShowKeyPlus - has proven more accurate than some other license key checkers).

EDIT : Who installed the original OS ? Sometimes commercial sources use a VLK to install and activate which won't work on any re-installation.