In some cases we have seen the preview window inside of Camtasia Studio editor go missing. Usually this is related to a setting in the program being corrupted and the Preview window is being drawn in a location we cannot see.
If you are on Windows 7, or Windows 8 there is a really easy way to get this Visible again:
Click on the Camtasia Studio window to give it focus, then press and hold in your windows key, and then tap the Left arrow button on your keyboard.
That should re-size and snap the Camtasia Studio window to the left side of the screen and also will get the coordinates correct for the Preview window.