This link is taken from the help thread (click on this link): LimeWire Pref Folder in Vista

Close LW completely & then follow those directions to find your preferences folder (which is named LimeWire). Delete that folder, then restart LW & see if it connects.

If it doesn't connect, go back & find the folder named LimeWire (you just deleted it but now there'll be a new one). Open that folder. Inside it will be a file named gnutella.net. That's the file that the original help thread If LW Will Not Connect tells you to replace. The help thread has links for downloading a new gnutella.net file.
Close LW completely before you replace the gnutella.net file.