Doors and Windows - wondows won't stay open

wood windows, doulbe-hung, with aluminum glides. I guess the sash weights or counter-weights are broken. how do i fix this? I have to prop windows open now or the crash down>

If you have aluminum on the side tracks, these windows use a spring back behind the aluminum to counter act the weight of the sash instead of a sash cord and cast iron weight. Sometimes the spring breaks, sometimes it just comes loose, sometimes the little plastic end on the spring that is supposed to catch at the bottom of the sash breaks.......in any case, repair is about impractical. You can either get new tracks with springs or bite the bullet and install replacement windows.