Usually I'd recommend updating your Java with thte newest version using the JRE offline installer. Then I'd reckon deleting the LW preference folder (the old one called " .limewire " and the new one (of version 4.12.) called "LimeWire", which is located in the hidden Aplication Data folder under C:\Documents and Settings\Administrator<you computer name>\Application Data
But since there are a view people who seem to have problems since the latest update to 4.12.3, I reckon you waiting till tomorrow until the brand new version is available and download it from here:
http://www.limewire.com/
If the problem still occurs after this update, then try my suggestions above.
