Go over to Connection Problems & read the sticky. The first part "... check here first". Make sure your software firewall's configured properly. Read the stuff about UPnP & if your router supports it, make sure it's enabled & used within LW's firewall config (in tools > options).

Read also about internal firewalls within modems/routers. If your modem/router has this, you may need to port forward manually. Do the port test & see what result you get.

What are 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

I see you've had this problem before
http://www.gnutellaforums.com/showth...202#post180202
http://www.gnutellaforums.com/showthread.php?t=49727

You must've fixed it before, as it's only been days since you haven't shared anything. Unless your hardware or something else has changed, just go through the same process as before!!