Have you made WMP your default player? Click on the link below for info
Setting default video app
If you still have trouble, you might have to change the file types that WMP associates with. Within WMP tools > options > file types.
Untick the file types that you want VLC to play > apply > ok.
*You'll have to preview with VLC by opening your incomplete folder outside of LW. For some reason, VLC won't let Windows users preview within LW!