Hello, I’m Nathan, and I’ll be assisting you today. My livelihood depends on your positive feedback, so your satisfaction is my highest priority.
Sorry to hear you’re having trouble.
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 functionality may be restored.
If no change, a replacement certainly may be in order: http://amzn.to/1QfUb9M
In that case, you don't have to worry. When you receive your replacement kindle, once it is registered and connected to wifi, all of your existing books/purchases will sync to the new kindle, so you won’t lose any of the content you’ve previously purchased.