What DVD player? What wifi network? If by PIN you mean your wireless password, then it's setup on your wireless router. Many routers these days come with a sticker with the wireless setup on it, including the password. If your modem doesn;t have one or it's been changed, then simply log into the router and change the wireless password to something you know (and save it in a safe place). If you can't log in, try the default userid and password for your router (see your manual), otherwise, reset the router to factory defaults and reconfigure as you like.
IF by PIN you mean the WPS PIN number, then it's on the device and must be entered into the router. Simply follow the WPS instructions in your router's manual.
Without know exactly what you mean or what router or DVD you have, it's hard to be specific here.