I've recently started having problems with video disappearing in Premiere. Usually happens when I have other cs6 applications open, like after sending a sequence to Audition, or using AE dynamic link. The program monitor displays a black screen, the thumbnails no longer scan, and the media encoder preview displays white noise instead of video. I have to force quit, and then if I try to restart Premiere it hangs up when attempting to load the Quicktime Bundle. I have to restart my Mac to get it working again.