You probably have a Java problem. Go to www.sunmicrosystems.com, and push the option that says "Download, or Get Java". If you download a new Java, that should get you into the chat.
while this is a Technical Issue, and should be in the Technical Assistance forum, let's see what i can do:
1: Mitch is correct with having the new Java. Try that.
2: If you use the Firefox browser, the new Java isn't compatible. dunno why, just isn't. if you have IE or Opera, they should work fine.