When LW pops up all the time (not just at system startup) & refuses to stay closed, it's usually caused by a worm.

Try the easy fix mentioned at the end of point 2 below, it's worked for a lot of people.
WARNING: Viruses on the network you should be aware of

If you need more help, there are links to sites in point 5 (Norbiesworld has helped a lot of LW users, but at the moment there's a long wait for help).

Always make sure that you're using a good AV program. Keep it updated & use it to scan downloaded files before you open them