can’t authenticate to PDC

My user let his password expire:: a sysadm reset him a new password, but his authentication is still failing( he is on a Win2K machine ):: he can access a share on the PDC by providing his credentials, but does not authenticate to the domain:: Another indentical computer on his same remote network authenticates fine:: we removed his computer from the domain, and now when we try to rejoin him to the domain it can’t find the domain controller, but we can ping him and he can ping us:: Event log shows a successful logon when he accesses the share with his credentials, so why does his system report the domain is unavailable or does not exist when we try to join his computer to the domain??