The preferences of the new version of LW (4.10.x +) may be found in another location. Use your search function, go to options & change view mode to show "hidden" files & folders. Then search for limewire
It's found here: C:\Documents and Settings\username\Application Data\LimeWire
The Application Data folder is "hidden".
You can see an example of how to find & delete it from a FrostWire example here: How to delete your FrostWire Preferences folder
But of course, it's the limewire folder you search & delete. Check that the one you select is from the above location (ie: within the Application Data folder!!!) And of course only do it whilst LW is "closed"!

I will soon be adding some examples & details about this in the link Only A Hobo left.