Block Alt-F4 in Delphi

procedure TForm1.FormKeyDown(Sender: TObject; var Key: Word; Shift: TShiftState);
begin
  if (Key = VK_F4) and (ssAlt in Shift) then
       Key := 0;
end;

How to Minimize All Windows

uses ComObj;

procedure MinimizeAll;
var
  Shell : OleVariant;
begin
  try
   Shell := CreateOleObject('Shell.Application') ;
   Shell.MinimizeAll;
  finally
  end;
end;