contact HP support directly and have the serial number and receipt for the rep if the serial number does not show as valid or recognized it may have several reasons such as not bought from HP directly or from a authorized 3rd party reseller or it may be a factory refurbished system that has a different warranty depending on if it was sold directly by hp or from a 3rd party seller
https://support.hp.com/us-en/check-warranty
https://support.hp.com/contact-hp
https://support.hp.com/us-en/document/ish_9335347-9335391-16
