Why is the casing not stable with one another

Is it like sitting in a chair with one leg shorter? If thats it then the case got bent.

This can happen when you pack your system is a case with other stuff and then someone sits or something heavy is placed on the case warping the frame from the in consistently of how the system is pressured.

If its just a little (less than 1/8" you should be able to torque it back with your hands just be careful as you can damage things if you go to far and don't twist the screen!

If its more than this you really need to dissemble the system down to the frame and then straighten it out. If you see any cracks or stress rippling then its time for a new case.