I have a file I have been using for months. Suddenly today whenever I select anything in one area Sketchup crashes. I have even gone back to copied files several months old and the same thing happens.
When you say, no copy you have always a copy each five minutes, and your file often begin by a tilde, or double tilde, in fact Sketchup make a save automatically.
So for the first time, try watch your file with a tilde.