Window falls when opened

It looks like you have a spiral balance system for a tilt window. It certainly appears one of your pivot shoes is broken; you'll need to remove an undamaged version and compare its width and thickness to our selection here to find a replacement. You may want to replace these spiral balances as well if the windows can't stay open. We'll need the length and diameter of their outer tubes, and a good picture of the tip. See the videos below.