When I try to start up Limewire, it seems to freeze -- but not quite. Buttons still highlight when I hover the mouse over them, but actually clicking on them gives no response. This includes the "Upgrade to LimeWire Pro" box at the beginning. I've reinstalled it a couple times, but nothing seems to help, and nothing on the LimeWire support site covers anything of the sort. What is going on?

Try updating to the latest version here (I have this one & LW's working fine): Java SE Downloads
or, if that one gives you any problems, try this older version, which has worked well for lots of people: Archive: Download Java 2 Platform Standard Edition (J2SE) 5.0 Update 11
Whichever Java version you use, download the JRE offline installer & remove any other Java versions before installing another one.

If that doesn't help, 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 change 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.
In case you have Vista: LimeWire Pref Folder in Vista