wirelss network problem

I had a cable broadband internet connection and attached a netgear wireless router to the cable modem and it worked great for the windows laptop and my macbook.
recently had an cheaper broadband connection (via the telephone) and have installed it(stupid mistake).... the netgear has been connected to the router sent by the company......
the windows based laptop shows 'connected but never connects to the internet macbook needs network diagnostics to be run every time it is switched on and off...
the customer helpline is just useless.
this is a pain .......
can help is appreciated!!
not very computer literate so 'easy english' explanations will be appreciated.