Could be a number of things causing it:
Lack of sufficient ram for both system & LW, Fragmented drives, too many share files, too many incomplete files, a version of Java that doesn't suit your system since some versions work better on some people's systems than others, LW preferences that are partly corrupted, a messy uncleaned system registry, cpu that is a little out of date for today's needs, security software that is interfering, ...