Dear Cheryl,
I feel a bit embarrassed at all I am writing on this site.... also I am just a beginner at ES (about a month's experience), so no expert. However when you ask, the universe delivers.... and the first response you have attracted .... is mine! Hope you feel heard!
The ES course is so rich in great exercises and insights, so I think you should not attach monumental importance to getting nothing on your theatre screen the first time. So what? Just get on with the course - you have 150 goals to generate next - and try again when you are ready.
Other ideas that come to mind. Trust that you are just perfect and what you get is perfect too.
If you try again and get a blank screen, you could take the blank screen as your symbol.... imagine the potential for expansion / development in having a blank screen to play with.
Or are you not a particularly visual type? Can you hear anything? Or try smelling?
If not, and you are getting frustrated and stuck, you could just be creative, trust youself, and actively choose a symbol, just to be getting on with.
I feel sure that once you are a little familiar with the whole visualise-a-symbol process, and are confident and trusting of the exercise, your theatre screen will be generating all manner of symbols.
From what I can see, Jack is providing us with several tools to get in touch with our inner wisdom / higher power and refine our life's purpose. Some tools will be more effective for some individuals than others. Find tools that work for you and celebrate your wins with them.
Good luck and happy visioning!
French Claire