VS crashing could be due to a variety of reasons. I've had it crash occasionally, as I think a lot of us have.
Could you provide us with a little more info to work with? What sort of video files are you editing? Right-click on a video clip in the the timeline or Library, select properties, and post them here.
Please complete your System Information
in your profile. Clicking on this button -->
will take you to a short tutorial, explaining how to find and complete that information. This way it will always be available, and will save you from retyping it in the future.
It could be that where you have designated your working folder, does not have enough free space, not enough RAM, conflicting with another program or a background application suddenly jumps to life stealing the resources.
Not that it's directly related to your issue, but keeping DirectX current seems to cure several problems with VS. Go HERE
and download the latest MS Direct-X drivers. The most current is dated November 2008