Luis,

This almost sounds unbelievable but don't give up just yet!!

You can try a few other things..

If you are using joystick, remove them and try a flight just with mouse and keyboard only.

Try to to remove all the other add-ons. Install only captain sim and see if that helps

If you are still in the same boat, then probably you need to start fresh. Reinstall FSX, download the CS 757 files again from this site using your profile and then install only captain sim 757 without any add-ons. Try with default cessna (engines off etc.)

Sorry, but can't think of anything else. If someone else has any other suggestion...