If you own a Kindle that was purchased in 2012 or before will NEED to download a software update or you will no longer be able to download Kindle Books, Access the Kindle Store, and more. According to the Amazon Kindle Help article.
If you do not update your device by March 22, 2016, you will receive the following message on your device: Your Kindle is unable to connect at this time. Please make sure you are within wireless range and try again. If the problem persists, please restart your Kindle from the Menu in Settings and try again. If you see this message on your device on or after March 22, you will need to manually install the latest software update for your device.
If you aren’t sure what version software your Kindle is running you can check the Amazon Kindle Help Article HERE to see exact directions on how to update it.