Ironically, when I reinstall the newest one (such as reinstalling O'hare) Quality Wings 757 becomes inoperable.
No, it doesn't. It's still perfectly usable, with just ONE issue: you cannot have the QW757 to be saved as a default startup airplane, because of the updates in the Esellerate SDK which happened almost 2 years ago that we had to support, but those required a small change in the QW757 Gauge code too, there's just nothing we can do to fix this on our side, while maintaining compatibility with the newest Esellerate library.
We explained this to Qualitywings a while ago, offering also our help to do the changes, assuming they were too busy with newer products.
However, they haven't show any interest to update the existing 757 so, until they'll finally fix it, you will have to switch to the QW757 only after having loaded another airplane first. Or, just load the QW757 AGAIN, if it's saved as a default airplane.