If you have the Pro 4.12 installer saved then try reinstalling.

Check this link for more info (don't worry about point 2 - you'd be downloading a basic version which would automatically uninstall your Pro version during installation!!): http://www.gnutellaforums.com/333278-post2.html

Just remember that unless you have the Pro installer saved, you won't be able to download that again. LW don't keep old installers available for download, apart from the previous release at the moment.

Not all preference folders are named .limewire - that's the name of the prefs folder in versions earlier than 4.9.34.
Prefs folder in later versions is named LimeWire... so make sure that you also deleted that folder