I presume that the q100 modem is a DSL modem?
Have you bridged the DSL modem if this is the case? It's preferred to bridge the DSL modem if has a built in router. Once it's bridged then you need to put in the PPPoE account information in to the 615 router under Setup/Internet/Manual. Power cycle everything then the router should get connected to the DSL modem and handle all the Internet traffic.