Are you connecting the LAN port of the modem to the WAN port of the router?
When configuring a router w/ DSL, how the modem is configured determines how the router must be configured.
If the DSL modem is configured as "unbridged", then it will be configured as PPPoE and will include the username/password of the account (if applicable). And your router’s WAN needs to be configured for DHCP.
If the DSL modem is configured as "bridged", then the DSL modem will pass the PPPoE requirements to the router, and it's the router's responsibility to configure PPPoe and the username/password. Problem is, most routers default to DHCP (not PPPoE) on the WAN.
So you first have to determine how your DSL modem is setup to determine how to configure your router properly.