netgear dgn1000 as modem, D-Link 815 as router

I am trying to use my DGN1000 (orange broadband) modem/router as a modem only (found the modem only mode no problem), but after connecting my Dlink DIR-815 router to the DGN (by LAN cable as instructed), I am unable to get my internet connection to work through it.

Bought the DLink as the Netgear range was so poor and signal strength drops away so fast that I have next to no wireless signal from anywhere in the flat apart from places with a completely clear line of sight.

Does anyone know how to connect the two so that my access point with be the more powerful DLink (which is a router only - no modem), using the Netgear in modem only mode?