PM sent. But...
You might be able to recover by doing a factory reset. That has the advantage of not opening the device, but you will lose everything. If recovering the books is important, you will need to open the device and remove the card and put that in a PC. If you use a Mac or a Linux machine, you should be able to mount the data partition and get the books. Windows doesn't like removable cards with multiple partitions and I don't know how to use it to get at the books.
Memory Upgrade Mod Guide has instructions that you can use to open the device and restore the image.