Hello, I’m Nathan, and I’ll be assisting you today.
Sorry to hear that you’re having trouble with this but I’ll do my best to help you out.
The book file format has not changed, but as of March of this year, there were some critical software updates required to be installed on all kindles, if that was not done, then the kindle is no longer compatible with the kindle servers and cannot accept new books until it is updated.
Please go into your kindle settings menu and tell me what it shows as the current software version.
Thanks for checking. 1.2.1 actually is the latest update, there are no newer ones available, but I believe support for that particular model has actually been discontinued at this point.
What we can try though is to reboot the kindle, then attempt to download, and even to transfer books manually as a next step.
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.
It should have either a push or a slide one,
but we'll move on then,
plug the kindle into your computer via usb cable
then sign in to your amazon account on the computer, and go here: http://amzn.to/2bO5NDP
Choose a book you want to download, click the box next to it and click actions, then download and deliver to, choose your kindle,
then watch for the saved/downloaded book file.
Open your computer/explorer/finder folder, and on the left column you should see the kindle "drive" appear, open that up and then find your downloaded book file, drag/drop or copy/paste it to the Documents folder within the kindle drive.
When you disconnect the kindle, the book should be in your library.
Because the 3g connectivity function is no longer fully supported and the new book files are typically larger (due to richer content), these older models are not supported any longer in terms of software updates, and so there will be limitations to what content it can accept.
You are seeing that on the kindle itself?