Try resetting the device by pressing and holding the power button for 20 seconds. Try turning it on after that. If it doesn't work, let me know.
It is a Kindle HD7 just to make sure?
Try a deeper reset. Plug the Kindle into the charger for 30 minutes. After that AND WHILE STILL PLUGGED IN, press or slide and hold the power button for 30 seconds. After that, try using it. Let me know the approximate purchase date if it still fails to function.
That should have resolved the issue. If it did not, you most likely have a failed Kindle, but it appears you are still under a warranty. Contact Amazon at(###) ###-####and they should replace it.