Has anything changed (hardware, ISP plan etc) since you were able to connect? Rather that turn off your firewall, it's better to configure it properly
Firewall setup

How did you have your router set up when LW was working... did you have UPnP enabled or were you port forwarding (or neither)? Have a look through this thread, it's got lots of info about connection problems. Do the port test & see what result you get. Do you see the firewall icon (brick wall)?
Connection problems? Check here first!

If you're still stuck, post back with your details

OS(Win XP etc)
LW & Java version (help > about LW & you'll see)
Firewall you're using
Modem/router brand & model
ISP
Connection type (DSL etc)
Where you connect from (home, school etc)
Are you sharing a connection with other computers
Is this your first try with LW