?
You will have to get the password from the person you bought it from. You will not be able to get the password to the administrator account without him. If he does not provide the password, get your money back. Knowing there is no other administrative account you can use or possibly any other account, you will not have full access to the computer, making it unusable.
Harley Drive
ask the seller , it is probably stolen if you bought it on ebay you can get your money back as it is unusable