look
here under
signing in online
once logged into your account, look on the devices button and click
Manage
login again
This shows the devices page. if there is a pc showing on this tab, click
Show details, then look on the info and support tab - is this your PC? if so, its likely that its linked to your account.
if no pc listed, licence could be linked to account of people who gave it to you.
If so, they can follow same steps and on the Devices page, click
More actions and Remove PC - this will mean the licence is tied to motherboard again. Perhaps not right away, I am not sure how fast that step takes. You will need to go through the steps in Barty's link to link PC to your account and then fresh...