Thanks very much to FOTH and LOTR for their suggestions! Unfortunately, it seems that the problems (and solutions) to somewhat similar problems on Windows machines are not applicable to my Mac's problem.

Let me add to my original post that I had been running LW with no problems for several months before this blank screen problem occurred.

Since my last posting I have re-installed the Mac OSX operating system, hoping that maybe that would solve the problem, but alas it didn't.

Any additional suggestions are eagerly anticipated!

-- David