the admin account might have been disabled for extra security. there are 2 possible situations here... the machine is standalone or it is in a domain. if standalone, just boot into the safe mode and then login as the admin (admin account is NEVER disabled in safe mode). once logged in just enable the administrator account. if the machine is in a domain, you can enable the account using the safe mode or by logging in as a domain admin. lemme know if this helped...