I've had my kindle stuck for hours and wasn't able to find any solution. Google was helpful a lot of times and it didn't disappoint me. so i might just as well do a quick post on this for those who are too lazy to read the manual just like me."
Kindle 2 or Kindle 3 reset: This is easy – just hold the power button (next to the headphone jack) for 15 seconds or 30 and the device will reboot.
If this doesn't help then try Recharging or or plug it to your computer for some minute, and see you'r little android back in action. Cheers!!