title_body: What are the actual on/off/sleep states for and how do you hard reset a Kindle WiFi?
upvoted_answer: As already commented,  plug in the Kindle 4 to the wall or your Mac/PC.  Let it charge for a bit -- even 15 minutes will help.  Leave it plugged in,  and press and hold the power button till the screen flashes. Wait a minute to see if it is doing a reboot. When that probably isn't enough,  do it again.  I've heard the number "5 times"  and I've experienced needing at least 4 times (actually, I wasn't counting).  The screen will flash, and after a few times of this,  it will finally continue past the flash and will begin a full reboot.
  
  After 4 or 5 of these freeze ups, I decided my battery might be aging, and started recharging it every night.  It can't hurt.  I also kept my eye open for a cheap spare K4, just in case.