Sounds like your router is running dhcp for net access, is it? If so then the computer you just setup will need to have a properly configured dhcp client and config file.You will need whatever user and password for that computer to connect to the router, if they are needed.Chances are the ISP you use is also the same way, but that isnt always the case. I use roadrunner and just a plain dhcp client w/o a password or user or even anykind of a client config file is needed.
The router connects to the ISP using dhcp, that sounds like it working ok, but on your lan or subnet the router also delegates Ip addresses using dhcp.