So you used this device to replace your ISP's modem?
It may be that you need to use the modem they gave you and then hook the router up to it. My network is set up so that the modem that my ISP (Verizon) gave me is connected to the wall jack with an IP of 192.168.1.1 and from there my router is connected to it and acts as the DHCP server so all of my devices are on the 192.168.2 subnet
I have a few other questions about the issue:
Did this start to happen immediately after you installed the new router or was it working fine at first?
Do any websites load or are they all failing?
What ISP do you use?
Also, is this the device you have? DGN1000
I'm trying to figure out exactly what device you have so I can give you better directions