1. Have you tried a SAFE Boot & repaired permissions? SAFE Boot & Repair Permissions or Resolving Disk, Permission, and Cache Corruption
2. How much ram & spare HDD space do you have on your system drive?
3. Which OSX version are you using? (find out under the apple icon at top left of menu bar, then choose About This Mac. And what processor speed do you have?
4. How long have you been using LW?
5. Which version of LW are you running?
6. If you have a lot of incomplete files, try Tip: Purge the Downloads Queue!
7. Go to your system folder, Library > Logs > CrashReporter & find a listing for LW & open it. Tell us what it says.