So I have a 4 hour long screen recoded video that I've been working on. I worked on a similar video a month ago and everything worked perfectly. Now on my 2nd video, everytime I do something like cut a part of the video to make a pan and zoom section or slide an audio clip just one second forward or add any new media to the time line, the whole thing crashes. I'm still able to save it and move around the time line, but the video screen is black and neither the audio or video will play. If I want to edit, I have to do one thing, save it, let the app crash, close it, open it up again and repeat.
First guess is that the codec or frame rate used by the screen recorder is a problem. But, since you say it worked before, my second guess is that you are running out of HDD scratch disk space or RAM due to the size of the project.