Stylus pen problem

I bought Huion H420 few months ago and decide to use it now. I can't use it. It told the tablet already applied and device already connected. I follow all the user guide but it doesn't help to solve. I even try to use on my ipad. It just appear stylus device is available. But when I try the pen on the table. It won't appear the light green button when I turn it on. I am so clueless.