In LW tools > options > advanced > system startup. Make sure that 'run on system startup is not ticked. If it's ticked, untick > Apply > ok.If that's not the problem, sounds like you have a worm.
Try this fix, it's worked for a lot of people.
The easy fix for Limewire popping up every few seconds (try this first)
If that doesn't help, there are links to help sites below
Spyware Warrior :: Index CastleCops® » Security Forums SpywareInfo Forum FAQ - SWI Forums
Always make sure that you're using a good AV program. Keep it updated & use it to scan files that you've downloaded
before you open them.