First thing to try is right-click LW & choose run as Admin. See if it opens. If not then reinstall all from scratch using this technique:
http://www.gnutellaforums.com/333278-post2.html 
(For Vista, both the installer & then the installed LW program should be set to run as Admin)
If still problems, check the topics here which might be the issue:
http://www.gnutellaforums.com/genera...ta-issues.html