Previewing themes, comes up blank

After installing the theme “Avada” from ThemeForest.net, I couldn’t see a live preview of the theme. I thought maybe it had to do with running 3.3.2, so I upgraded to 3.5, and now all of my themes won’t show a live preview. I tried reinstalling 3.5 through Dashboard. Any thoughts on how to fix this? Thanks!

Eric Hartmann