What are your details?

OS(Win XP etc)
LW & Java version (help > about LW & you'll see)
Firewall you're using
Any other security you're using (antispyware, worm protection etc etc)
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

What happened before LW stopped working? Any changes to hardware, software, ISP etc.