Check that your router or modem is forwarding the port LimeWire is using.
PortForward.com - Free Help Setting up Your Router or Firewall

To block the scripts and ads that sometimes pop up, go to the internet options control panel,
switch to the Security tab and add *.bearshare.com and *.fastclick.net to the Restricted Sites zone.
Blocking Fastclick alone will stop a lot of ads on a lot of sites.