Dell Studio 1735 problems connecting through wireless.

Please can any one help? I have a Studio 1735 with Vista software and love it, have had no problems untill now, connecting to the internet by cable modem is fine and have just bought a Belkin N+ wireless Router, followed set up instuctions by the book, set up security no problem, computer said everything is connect and i'm ready to use, also set up two more laptops, one has xp and one has vista which is also my software too, but when i take my cable modem out after setting everything up my computer won't connect, but my wifi and Belkin symbols say i'm connected,the other two laptops connect fine no problems please can anyone help?   Many thanks Sarah