I have a 2600G which I can ping - and is working fine - ie ADSL / VPN etc.

However, when I open a browser and enter the IP all I get is either a blank page returned, or a failure to return anything (not responding).

Hence the pop up to allow me to log in doesn't arrive.

The router has been restarted - and attempts to open the login have been made with different browsers and different PC's.

Any clues ?

try chnging your pc network interface from auto-negotiate to 10FD and see if it maje any difference.

See if you can telnet into the command line interface.

telnet 192.168.1.1 ( or whatever the router IP is)

that might tell if it's just the http or a problem with the router responding.