There should be a default local admin account called Administrator. Try logging into it. If you're lucky, there won't be a password on the account. If there is, try downloading a program called Konboot. Konboot allows you to type in any password at the login prompt for any user account and get access to the computer. I don't think I have to mention (but I will anyway) not to do anything illegal with this tool. You, and you alone are responsible for what you do with it.