Intermittent broadband and problems setting up a borrowed technicolor router

[#1]

Recently my broadband started dropping connections a lot, so I thought the most obvious suspect is my aging Netgear DG834G router. I have borrowed a Plusnet Technicolor router to test this theory but I cannot set it up. I did a factory reset on the router as it had my friends login details etc before trying to use it.
I see the Broadband Setup page when I open my web browser, I enter my account username and password, I click Go and I get a big green tick. Just like it says in the guide.
I then open a new tab and try to navigate to google, where I'm presented with the Broadband Setup page again. I've been round this loop 3 or 4 times now and I have no idea why.
I'm back on my flaky Netgear for now but would really like to try out the alternative router to troubleshoot my intermittent broadband.

[#2]

@ NormW
The serial number for your friend's router will most likely be linked to their account so factory resets will be pulling their details down.
This just means you'll need to log into the router and update the details to your username and password manually:
http://www.plus.net/support/broadband/hardware/plusnet-2704n-advanced.shtml

[#3]

Your friend should have disabled automatic router setup on their account before giving you the router. You need to forward this link to them: https://portal.plus.net/automatic_hardware_setup/index.php

[#4]

OP, a similar thing happened to me when I bought a used PN router. What I did was to log into the router (via 192.168.1.254) and then click on 'Connect' (on the main page I think).
I'm sure that's what I did to resolve the problem.