Hi there! My name is***** am a computer professional with over 15 years of experience with both Mac and Windows computers, phones, tablets, and printers. It would be my pleasure to assist you with this.
Please login to your account at Amazon.com. Select YOUR ACCOUNT. From the drop down menu that appears, please select MANAGE YOUR DEVICES AND CONTENT. On the page that appears next, you will see a CONTENT Tab and a DEVICES Tab. On the CONTENT tab you will see all of your Kindle book purchases. You can sort them by title, author or purchase date. Please locate the book that you want to download to your Kindle, select it by checking it and then click on the ACTIONS column. Choose deliver as the action. Select your device from the Device list. If you have more than one Kindle, make sure that you choose the Kindle that you are actively using. Don't select the Kindle Cloud reader unless you have downloaded the Kindle Cloud Reader APP to a computer or device other than your Kindle and wish to read it there.
If you still have issues after following these steps, you may be nearing full capacity on your Kindle, and may need to delete a few of the books that you have already read. The books that you delete from your Kindle will continue to be available at the Amazon website under My CONTENT if you should wish to download them again at some point in the future.
Please try this and keep me posted.