procedure TForm1.Button1Click(Sender: TObject);
var
hSysMenu: HMENU;
begin
hSysMenu := GetSystemMenu(Self.Handle, False);
if hSysMenu <> 0 then begin
EnableMenuItem(hSysMenu, SC_CLOSE,
MF_BYCOMMAND Or MF_GRAYED);
DrawMenuBar(Self.Handle);
end;
KeyPreview := True;
end;