The program crashing may be caused by one of several factors for which we need more information:
Computer specification and program version, see this topic for what is required and please quote processor and graphics card make/model in full, and if a laptop, what monitor/screen resolution(s) your are working with.
I would suggest you put this information in your profile signature so we do not have to keep asking for it.
Are the graphics card drivers up to date?
A screen shot of the Program settings, Device options tab would help.
What format and resolution video files are you working with? If you do not know, download and install MediaInfo and analyse one of the clips and post the results, see this tutorial on how to setup MediaInfo and analyse a video clip for all the data required.
The amount of free space on the hard drive(s) you have.
Was there any error dialog that popped up when the crash occurred, if so what was the full message?