Hello Mary. The problem seems to be with the hinges. If you get a bank card and slide it in to the back of the windows does the rubber gasket grip the card. If not then the hinges have worn. How old are the windows? The hinges will be top and bottom on a side opening window and left & right on a fanlight window.
To replace these you may have to call upon a double glazing repair company-= but dont get ripped off.
Paul
March 2011