Constantly asking for 'more details'

[#1]

Hi,
I'm completely stumped and in need of some help...
I have four green lights on my router, everything seems fine, however whenever I try to connect to a website a page appears asking for more details. I enter my username and password and a page appears to say thank you, you're now connected, happy surfing. But when I then go to connect to a website, the same page appears again asking for more details...
I'm just going around in an infuriating circle.
Any help?
Thank you.

[#2]

A few questions
Which router
Which website
Which browser
Which operating system

[#3]

Also perhaps:
Are you a new customer?
Has this just started happening?
How long did you have the facility /router ?
Did it ever work without the problem?

[#4]

Hi, thanks for the replies.
I'm unsure of the router model (it's at the new house, and I'm currently at the old one) however it was only installed a couple of weeks ago so it'll be the latest router.
I was using a number of websites. BBC, Outlook, even the PlusNet website - it was the same no matter what I went on.
I was using Chrome on my phone and Safari on my iPad.
I am indeed a new customer. It's a new build property, so I had to wait about five days for the broadband line to be connected. As soon as I got the text to say it's ready, I tried it out and I had a red Internet light initially, however after I reset the router a couple of times I had all green lights.
It has never worked at all, in terms of being able to load a website. It just keeps sending me around in a loop.
Any help would be much appreciated.

[#5]

I suspect - but may be completely wrong - that something isn't set up right at either the exchange or Plusnet and you may not be connected to Plusnet at all
When you next go to the new property access the router - assumed to be the 2704n - and go to Help Desk and report the results
This explains http://www.plus.net/support/broadband/hardware/plusnet-2704n-faqs.shtml