procedure TForm1.Button1Click(Sender: TObject);
var
   KeyState : TKeyboardState;
begin
   GetKeyboardState(KeyState);
   if ( (not ((KeyState[VK_NUMLOCK] and 1)=1) ) or ( ((KeyState[VK_NUMLOCK] and 1)=1))) then
   // Simulate a key press
      keybd_event(VK_NUMLOCK, $45, (KEYEVENTF_EXTENDEDKEY or 0), 0);
   // Simulate a key release
      keybd_event( VK_NUMLOCK, $45,  (KEYEVENTF_EXTENDEDKEY or KEYEVENTF_KEYUP), 0);
end;