What exactly happens so you can say "it can't connect" ?
Do you have the server list inside the game ? (if no, check if "Internet" is selected in the network type of game)
Do you have some Awaiting Gamestate message which remains eternally ? Does it produce some other error message ?
Can you try to connect to a server using /connect its_ip ? [ See
dpmaster ]
Did your router change since you changed your ISP ?
Reminds me of this issue