Hi, I'm Nathan.Sorry to hear that you're having trouble with this but I'll do my best to help you.
This symptom can indicate several possible issues: an internal hardware failure, a low/faulty battery, or just a simple memory/firmware glitch.
The first step here will be to attempt to reboot the kindle. This is done by pressing/sliding and holding the power button for 20+ seconds, or until the screen flashes (usually with an image of a tree), then release. Give the kindle about a minute to start back up, and let me know if the problem persists, we can then try some further steps.
Note: Timing is critical here, too long or too short won't work, use a timer if necessary, and be sure you are holding the power (not volume) button, and if there is a case/cover on it or charger connected remove all. You may need to repeat this process 4-5 times before the reset takes effect.