I bought a used PS3 from GameStop and I did the factory reset but every time I go to set a passcode on it, it still asks for my old one (which for obvious reasons I don't have)
The PlayStation website states that if the system is reset to factory defaults the PIN is set to 
Change Password Change the password required to adjust system settings. A password is required in the following cases: When playing content with parental control restrictions When changing the system's parental control level or Internet Browser Start Control setting When starting the browser with the Internet Browser Start Control setting set to [On]. When changing the current password Make a note of your new password. The password is set to  in the default settings. Hint If you select (Settings) > (System Settings) > [Restore Default Settings], you can reset the password to . Note that all other settings will also be restored to their default values.