the easiest way is to log onto the router locally , so if you do not have a pc connected to the router, take the router to a pc. connect a ct5 cable between the WAN port and the pc, nothing else. You may want to reset the router, in fact i would. then from the pc connected directly to the router. I would open a comand prompt. type in ipconfig /release , then wait for results, type in
ipconfig /renew , take note of the ip address, also take note of the gateway address. You then will go to your browser on the pc connected to the router. start IE click on the little red x in the top task bar, type in the gateway address into IE s address bar, click go, each router password / user name combo is different. fot each router usually admin password, (nothing) password, administrator password. You have to try or go to the manufacturers web site. First you want to make sure you can connect, then set security WPA is better thab WEP.
the pc you were using, when you connect it back, do a release / renew on that.