You say you see the dialup box---how far do you get .Does it go as far as verification of your password?
A couple of quick things to try
open internet explorer,then go to tools,internet options,connections and see
if never dial a connection is checked.
also if you do not do this already try to connect by using start,connect to and double clicking you isp icon.
See what happens then.
Apologies if this is a bit simplistic.
By the way you say your modem is ok--how do you know?