AppleGwava says it all. We can't see proof of ownership so we can't assist with password issues. Take the machine to a professional PC fixer and prove it's yours and he or she might be able to help.
I say "may" because passwords are there to protect data and you may lose whatever data are in the hard disk if the only answer is to take the machine back to the factory settings.
I won't close this thead yet but be careful taking any advice you might receive in case I don't see it first.