//Выключение курсора
procedure TForm1.Button1Click(Sender: TObject);
var
  CState: Integer;
begin
  CState := ShowCursor(True);
  while Cstate >= 0 do
    Cstate := ShowCursor(False);
end;

//Включение курсора
procedure TForm1.Button2Click(Sender: TObject);
var
  Cstate: Integer;
begin
  Cstate := ShowCursor(True);
  while CState < 0 do
    CState := ShowCursor(True);
end;