When someone opens my application it's full screen. All fine, except the problem is when someone clicks ALT + F4 this forms closes and all tables, forms,... are seen which confuses some of my experienced users. How can I disable that they will close form with CTRL + F4 and if there's any other command which causes form to close? I tried to use on key down in form event but it doesn't react, only if I use the code on some text box, not in form itself.