The number of downstream devices should not matter here.
Assuming that your DSL modem and service does indeed use DHCP, you might need to reboot your DSL modem so that it will clear the association with your previous router and then it can 'learn' the new one. Cable modems are known to need this type of action.
Try unplugging both your DSL modem and the router. Then plug the DSL modem back into power and let it fully boot. Once it is up, then connect your router's power.