Are you trying to configure for PPPoE and can't connect with your Internet Provider?
I haven't had much experience with Linksys, but I do know they have a power down cycle after you configure it goes like this
Un-power all devices and your PC.
Connect an Ethernet cable from the DSL modem to the Internet port of the Linksys Router/IAD. Keep the Ethernet cable from the computer connected directly to the Linksys Router/IAD. Power on the DSL modem, waiting until it has had an opportunity to resync with the DSL provider. Observe the indicator lights located on the modem and wait for the lights to stop blinking. A light indicating Power as well as DSL (or Internet, Online, Ready, etc.) should become solid to indicate that a connection to your Internet Service Provider has been established. Next you should power up the Linksys IAD/router waiting about 15 seconds before turning on your computer.