I had to do a house call for some Kindle support yesterday. All my friends know I go way back with the Kindle (the Kindle Touch is my fourth Kindle; I have had every model except the DX and the new bare-bones Kindle, which some folks are calling the Kindle 4) and they often ask me for advice on what to buy and how to do things on the Kindle.
Anyway, my friend had had her Kindle 3 for almost two years and had had no problems, but she said suddenly it wasn't charging. She was about to go on a bus trip, so she had plugged it in to be sure it was fully charged, and the little yellow charging light did not come on. When I went over there, I discovered the Kindle was in sleep mode, and would not come out of sleep mode. I plugged my own charger in to be sure my friend's charger wasn't the problem, and still no yellow light.
I suggested rebooting it, and discovered she didn't know Kindles could be rebooted. eInk ereaders are very easy to use, and pretty much single purpose-built— reading— but they are basically very simple computers with operating systems. Kindles run under a Linux operating system, and truly geeky types have even hacked them to do other computing tasks not sanctioned by Amazon.
The Kindle 1 was rebooted by sticking the end of paper clip (or something similar) into a small hole on the back, but ever since the Kindle 2, this function has been accomplished via the power switch. On the K2 and the K3, you slide the power switch to one side, but on the K4 and the KT, you press it. To reboot, you simply slide or press and hold the power switch in place for about 15 seconds, and then release it. It can take a few seconds to see a response, but the screen will go blank and then you'll see the entire screen become the Kindle logo (someone reading under a tree) with a progress bar that advances as the reboot progresses.
In my friend's case, once her Kindle 3 was rebooted successively, the yellow light came on, and a minute later it turned green, which told me that the device had in fact, been recharging all along, but because it was hung, the light had not come on.
My friend was good to go and all set for her bus trip.