Proving ownership of Imac computer without receipt.

My friend got a computer from his boss about 10 years ago for Christmas. He started having trouble with it and tried to wipe it and re install the operating system. He tried to put Maverick and it would not take it. Now all it does is boot up to a folder with ? mark. He decided to just buy a new computer and gave it to me. All I can get to by holding command and R is lock screen that needs password. Tried Option Command R, as well as Shift Option Control R and still gets lock screen. He does not remember that password, and his boss does not keep records over 7 years. Is this computer just a big paperweight now, or is there any other way to prove ownership and save this computer? It is a model #A1418