Double pane windows are made by glazing 2 windows together, spaced with aluminum square stock filled with desiccant. Once the seal is broken between the panes, the desiccant fails and the windows fog. There is NO way to repair these windows and the glass must be replaced! If you are the orignal owner of the house/windows, call the manufacturer and find out what their warranty is. If not call a local glass shop to replace the windows and purchase their extended warranty.