Hi, We are just setting up a 2850VN, ADSL connection to Demon ISP.

The router has a fixed IP address. The settings to the ISP are configured correctly. When the ADSL cable is unplugged I can connect to the admin page no problem via the network. Once the ADSL cable is plugged in and connected to the ISP we can no longer connect to the Fixed IP address via the network. Can't ping it, tracert it or anything. any quick tips (Small business with little networking skills)

Many thanks.

EDIT
Try first ip config release/renew ip address from the computer you can not log in

it looks like the fixed IP address of the isp have changed to me one you plugged back in the cable
If this is the case then you may need to obtain IP automatic or dynamic at wan >> internet access
Has your isp give you static or dynamic ip???(not the router)

Hi.

IP Address is static for ISP. We are also running ISA Server which is doing all the routing / NAT work, with our original router looks like it's just acting as a bridge to the ISA server's external interface (which is the the public IP address from our ISP.) The service from the ISP is NON-NAT and we only have a single public ip address.

Giving the Vigor the same settings as our existing router, we can get outbound traffic but nothing is inbound anymore even though the firewall etc are turned off. DHCP is served by the Microsoft SBS server so the vigor is not doing any DHCP allocation. Example config would be

Public IP xxx.xxx.xxx.154 from the ISP
ISP also told us to give the router the IP address of xxx.xxx.xxx.153
Microsoft SBS Server is xxx.xxx.xxx.154 on it's external NIC, gateway is xxx.xxx.xxx.153 (The router)
Microsoft SBS Server is on xxx.xxx.0.5 on its internal NIC

Is the problem both the router and the ISA are NAT'ing? (Again sorry for the limited knowledge on networking - just a small company )

Regards.