Do you remember having set the path to LuxRender when running LuxBlend for the first time? If not, the script can not be started automatically. Also, you didn't by any chance unclick the "run" button, did you?
If you deselect the "def" button, LuxRender should save the required files to any location you specify. You could try starting LuxRender separately and opening the files created by LuxBlend; that may make it easier to figure out what the problem is.
About Blender freezing: it's probably a good idea to start Blender from the terminal (just open a terminal window and type "blender"); that way any error messages will be visible. If any error messages are produces, just post them here and people may be able to help.