Try setting it up manually. First make sure the switch on the router is not set to bridge or auto and make sure that you have a computer hardwired to one of the four LAN ports. Then follow these instructions:
For Cable:
First, unplug the cable modem from power for at least 5 minutes. While it is unplugged, log into the router ( http://192.168.11.1 ) and go to Advanced->WAN Settings->WAN Port. Set the "Method of Obtaining IP Address" to "Automatic via DHCP" and Apply the setting. After the setting is applied and the router finishes rebooting, unplug it from power. Plug in the cable modem to power and wait for it to fully boot up. Plug the WAN port of the router into the cable modem and then plug it into power. Once it finishes booting, check to see if you can get an internet connection.
For DSL:
There are two types of DSL Internet Connections: Those which use a username and password, and those that do not. Which type you have determines how the Buffalo router should be configured. There are instructions below for each type of DSL connection. If you are not sure which type you have, you can contact your Internet Service Provider, and verify which type you have.
Physical connection The DSL modem needs to be connected to the WAN port on the Buffalo router, and your computer needs to be connected to one of the four numbered ports on the Buffalo router. The Power LED should be illuminated. The Wireless G led, and red DIAG led may be on. There should NOT be a green bridge led illuminated (it looks like a green arch). If there is please let us know.
DSL that does NOT use a username and password
First log into the Buffalo router ( http://192.168.11.1 ), the username is root, and there is no password by default; so you can leave it blank. Once logged in, click on 'Internet/LAN'. Set 'Method of acquire IP address to' 'Acquire an IP Address Automatically from a DHCP Server', and click 'Apply'. When the router finishes restarting, check to see if you can get online.
If you are not able to get online, goto 'Diagnostic'. On the Diagnostic page, click on 'release'. Then unplug the power from your modem for 5 minutes. Once the DSL modem has been power off for 5 minutes, power it back on. On the 'Diagnostic' page, click on 'renew'. Wait about 30 seconds, and try getting online.