I've tried but still have connection problems (OS X 10.6.2 (Leopard))
 

My computer died on me, and I had to get a new one. One of the first programmes I downloaded was LimeWire, but can't get it connected.
I have tried all that you suggest, and nothing seems to work. I have no idea what to put in my router settings. Here are my details. I really hope you can help as I used LimeWire for years on my old computer, and will really miss it.

Programme & OS:
Limewire 5.4.6
Java SE 6
OS X 10.6.2 (Leopard)
It's a new problem, with a new computer.

Computer:
Firewall - OS X - LimeWire allowed
4GB Ram
935 GB hard disk space available
No AV software

Network:
DSL Broadband
Netgear DG834PN
Home use
Eclipse.co.uk
UK

Other:
I'm sharing with my laptop, but I only use one at a time. I do use Vuse at times, with no problems.
UPnP enabled
I'm using a new, updated computer and I downloaded a new copy of LW.

What have you tried? :)

I have tried the things you suggest i.e.

DISCONNECT/RECONNECT LW
CHANGE LISTEN ON PORT
DELETE LIMEWIRE'S PREFERENCES FOLDER
DISABLE ULTRAPEER CAPABILITIES, DHT & TLS
Checked I have the latest JAVA
I uninstalled and reinstalled LW.
I have 'allowed' LimeWire in my system firewall.
I checked my router, though I have no idea what I'm checking for there. There are no entries at all in the firewall there.