So you now have the 4.12.6 installed?

Try this first, sometimes preferences can get corrupted after switching from version to version & it can lead to connection problems.
Delete LW's preferences folder when LW's properly closed. See point 3 here & also point 2 if you've used older versions of LW in the past (there could be a folder in either location).
Fixes for LimeWire
This will kill all of your settings within options, you'll have to go back through afterwards & reset things. If you're not sure of your settings, go through LW's tools > options & write them all down, so that you can reset things later.
LimeWire Pref Folder in Vista

If that doesn't fix things for you, please give us your details
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