My dad got a mac but hardly uses it so gave it to me. i changed the admin user from his to my name but didn't add a password for it. however, when mac went on sleep mode and came back on, the login pic shows my dad's name and asks for a password but his password doesn't work anymore. I have absolutely no idea how to get through or even shut mac down. The only option I see below the small login window is cancel. PLEASE HELP!! I've tried 1234 and 0000 as suggested by someone but that didn't work either. I'm a completely new mac user so I really know nothing.