Ok this sounds like a second hand office pc.
I think it was on a LAN before, and now its being used has home pc.
Or when you set up the windows sofaware, you ticked a few of the wrong boxs.
All you had to was del user accounts in control panel and tell the computer that there was no need for passwords.
Never buy a second hand computer, there nothing but trouble.
You can buy a new one for less than £300