   FullScreen Switch with Alt-Enter
  Hi, in my program made wth Direct3D 9, when the user press the alt-enter keys the program goes windowed or fullscreen depending on the case. This is ok, after some hours I made it work... The problem is that the system beeps after each mode switch and I do not want this.Let me explain how I did it: there are two hidden windows, one popup window for the fullscreen mode and one overlapped window for the desktop window (windowed mode). After that key press, the windows are switched and only one is shown. I made it this way (with two hidden windows) because my program needs to remember the restore state of the desktop window. My program watches the keys with the window procedure (it does not use keyboard accelerators).My question is why is so common in these cases, the system to beep and how I can make it function properly. I can suppose the problem is with the key presses, but I cannot found any system message to work with the problem. Any help or tip for this type of procedure is welcome. And excuse my english, I am learning yet.   