AFAIK there's no firewall in that modem. In LW go file > disconnect. Wait a couple of minutes then file > connect (sounds too obvious I know, but sometimes it works!).

Also go to tools > options > connections & make sure that 'connect on startup' is ticked. If it's not, tick it > apply > ok.

Also delete LW's preferences folder when LW's properly closed. See point 3 here.
Fixes for LimeWire
This will change all of your settings within options, you'll have to go back through afterwards & reset things. If you're not sure of your settings, go through LW's tools > options & write them all down, so that you can reset things later.