SOLUTION for power button not working,
Take apart your Kindle by watching this video (or another one if you have different model): https://www.youtube.com/watch?v=IpdMFIs0...
Clean and brush thoroughly metal components around and behind the power button, as well as related parts on the motherboard. Put it back together.
If this doesn't help, you can just turn off your screensaver, so you won't need your power button:
Get out of sleep mode by removing your battery, or by connecting your Kindle to computer by USB cable.
On Kindle 3, go to the home screen, press Del Sym, type ";debugon" and press enter. You will now be in debug mode.
Again, press Del Sym and then type "~disableScreensaver". You now have disabled screensaver. To enable it again, you will need to press Del Sym and then type "~resumeScreensaver". To get out of debug mode, type ";debugoff".
NOTE: you do not enter the quotation marks!
On Kindle Touch, just enter "~ds" in a search box, you don't have to get into debug mode. You are disabling screensaver and sleep mode by doing this, your power button will stop working as well. To enable it, restart your Kindle by using Menu. I don't know the command.
P.S. Note that disabling sleep mode will cause more battery drain.
I hope it helps.