I'm sure most of you know, but it's worth saying that Google and You Tube are two of the best places to find answers to maintenance and repair problems.
My Kindle stopped working recently (a disaster for an avid reader). The battery wouldn't charge and I couldn't get it to turn on. After doing some research (Googling) I found that by pushing the on/off button for 30 seconds it would "reboot" the device. Hold the button down and count to 30 slowly. It works fine now.