as 8tops and chucklz said, you may have a loose plug, if you do, and if you have tried the brute force and stupidity solution, this can complicate it by putting a ding in the 45 degree slopes of the key.
notice that your key has a bunch of angles on it like ///// at 45 degrees, these help you put the key in and behind every one of them, there are angles like this \\\\\ made only for pulling the key out, if you were forcing a stuck key before pushing in on the plug, you may have made part of the \\\\\ into \\ll\ which either means your screwed, or if you are really cleaver, you will cut a blade with a \ tip on it from some really thin material like the spring in a tape measure and you can put this in beside the key and lift the pins that your key no longer can lift.