How to windows 2000 professional

So, I bought a computer from a company that is going out of business and they told me the computer did not have a password… well it does, and now I want to know what can I do to use the computer… I called them they gave me 5 different passwords and none of them worked. Is there anything I can do to use this computer? It does not matter if everything they had there will be deleted I just want to use this computer. It is the administrator password’s I tried even loging in by putting guest and even leaving it blank but no luck… please some help! Thanks.