My parents have a bunch of Anderson 400-series windows in a sun porch. Below are pictures showing the problem. The windows are no longer hung straight, causing them to drag on the frame and become very hard to close. In the picture, there are four windows in groups of two (the right two are a set, the left two are a set)
I am not sure how just one window of each set doesn't work properly, especially because the entire unit is attached to the house via a nail flange on all four sides of the window.
What can I do to fix these windows so they operate as they're supposed to?