My Macbook asks for a password when trying to hard reset / factory reset

I have an old Macbook and I am trying to hard/factory reset it. I am using the method where you turn it on while holding down the option key or command key and the r key while restarting it. Every time I do this a gray screen with a darker gray lock symbol shows up asking me for a password. None of my passwords are working for this, and yes, I am using my admin password. I don't know why I can't unlock this screen, has anyone had this issue/know how to fix it? I really need to reset this computer. I have so much downloaded on to this and I have no clue what half of it is, it's so slow I can't do anything on it. Please help!