Can you give us a total desciption of your set up:

1. What firewalls you have?
2. ram?
3. HDD space available?
4. Connection type? (eg: dialup, broadband, cable, etc.)
5. Modem & router brand name & model numbers?
6. Where are you trying to connect from (home, school, work, etc.)?
7. What version of Java do you have? (Go to LW's menu Help>About LW...)
8. Who is your ISP provider?

Very mysterious that it's suddenly stopped like this. I wonder if your ISP has coincidently applied a filter of some sort.

I'm just wondering if it might be worth changing your Java. This is purely a stab in the dark but it might trigger something. If you have Java 1.5 then go back to 1.4.2 or vice-versa.
Sun 1.4.2: http://java.sun.com/j2se/1.4.2/download.html (Choose the JRE) OR Java 1.5 (take the JRE)

Are there any other programs you've installed lately or updates?

Another thought is to do a system maintenance & check your system over & defragment your HDD.