there are several possibilities, maybe you did nto config the router for the iSP correctly ie older dsl has PPPOE and you have to set that up and provide a username and password, its generally a software app on a computer, the router has a config section, etc.. And your sure its a router and not a switch or something, most residential ISP's just give you one IP address and the first device to get a connection to a non-gateway device is the winner, it i will connect no others will if you ahve a gateway device it gets the IP and manages your private network allowing multiple devices to connect through the ONE PUBLIC ip the isp offers.