Have you made sure that you're only running 1 software firewall & that it's still configured properly?
Firewall setup

Are you port forwarding through your router or do you have it running with UPnP enabled (or neither)? Just double check your router config.
Do this test & make sure LW's default port's not blocked
http://www3.limewire.com:6346

Has any hardware changed? ISP plan change? Are you using any other p2p apps & if so, do they connect without a problem?

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