Having been with BT for years using a home hub 3 for broadband I've switched to John Lewis for phone and broadband. Having plugged in the sagemcom 2704n supplied by them my windows xp desktop won't connect to the internet. My tablet/phone do over the wifi. The guy on the help line say the problem is with my computer and I need to [pay to] update my computer.
(If I'd known it was going to be a problem I'd never have switched! - "If it ain't broke don't fix it")
Rob, simply connecting the Ethernet cable from the router to your desktop is normally all that's required to get an Internet connection, so as beeuuem~2 asked, what goes wrong exactly? If you get any error messages then post the details in full.
By the way, for your setup you don't need to enter any passwords. If you start fiddling about with passwords in the Network section then you'll only make things worse.
When I try to connect it just says it cannot display the webpage.
Diagnostics give HTTPS Error 12029 A connection with the server could not be established, then HTTPS Error 12157 An error occurred in the secure channel support. There is also 'Could not make an FTP connection'.