Help needed, passwords dismatch problem

[otzo111]

Hello,
I got my Mini a month ago, the former owner did has its own password to be the administrator. I got this from him and did change it imidiately to my own, but just there for the administrator, so that I can install some programs

Yesterday I "found" the program Onyx and was looking how it works. I think, there I did do something in the accounts, because there were still stuff from the former administration, such like, that the former was still the administrator. I thought everything is fine and shut down my computer.
Than today, I tried to start my Mini, but now suddently (Never before!!!) I have to put some name in a window, and also some kind of password. I did ask the former owner, did this happened to him, he denied it and he couldn't help me.

I did try to start the mMini with help of the the CD (those with the Mini delivered) for many times, but always the "stupid window" opened, wherein I have to fill that name and password, which I do not know. I already tried all my combinations with big and small letters, etc., but nothing fits.

SO what can I do???
I can start the whole operation from the first, there is yet nothing I have to have safed, therefore I can start from the first installation.

Could somebody inform me, what to do?
THANKS Otzo from Finland

 

[Soulwar]

Ask the previous owner for their username and password. Username for the first line and his password on the second. You can try your password as well, since you changed it, if it's not working.
Then check the preferences that are set for Accounts and Login Options.
Launch System Preferences and go to Accounts. You can see if you are the only user or not and can delete users as well. Highlight your account and near the bottom left is Login Options. Select it and check the preferences and change how you want it to be.