Could be your router. Did you create an exception for LW in your firewall? Best to only use one software firewall; Setting up an exception for LimeWire in your software firewall (click in link)

Other than that, we need some more details about your set up: System details - help us to help you (click on blue link)

Using an older version of LW, you may need to replace the gnutella.net file, see If LW 4 Will Not Connect (click on the blue link)