2 options:
1. Close & reopen to see if it does the same thing.
2. Try deleting your LW Preferences folder whilst LW is closed; instructions here: Fixes for Limewire

If still problems after that, it might be related to the version of Java you're using. If you're using Java 1.4.2 then install version 1.5 or if you have 1.5, then uninstall it using add/remove control panel & install 1.4.2 instead using the techniques suggested in the above link.