The essential preview screen above thumbnails does not open, is not displayed, and cannot be located. The computer is WIN 7, i5 core, more than half the hard drive remaining. Only thumbnails show. Program was purchased online and no disk exists. The program being built is currently 17 minutes long. Thanks.
Sounds like the preview monitor has been moved off screen - try resetting the Window arrangement by pressing f9 or selecting Window, Window arrangement, Rest window . . . - the preview screen should reappear.