If you had DSL service with AT&T and now want to use the router with Cable, I suggest you reset the router to factory settings. There is a small hole in the back that has the reset switch. With the power on use a pencil or pen to depress the switch for 30 or 40 seconds. Then carefully follow the Cable company's instructions on the sequence for reconnecting the the modem/cable box and the router. You can also download instructions from the D-Link seb site.