What processor does your computer have and how much RAM?
What model of camcorder is your video coming from and what format and resolution is the video?
When you first add a clip of this video to your timeline, do you see a yellow orange "render" line over the clip? This render line indicates that your project settings are not set up to match your video specs -- and that can result in poor performance and a memory overload.
This is a guess, but I think I recall others with Xeon processors doing this.
In Edit > Preferences > General is a check box labeled "Use Hardware Acceleration". However you have it set, change it and try editing.
Meantime, switch to Expert view. You won't see the yellow orange line in Quick view.
This definitely sounds like a soft render memory overload issue.
(Though you should definitely also consider Bill's advice, should my line of questioning not pan out.)