I've experienced similar problem with mu Aura HD. Similar, since it was not a constant loop, yet after starting the device sometimes it rebooted immediately and some other time I was able to get the main screen and even open a book, then it restarted or went to sleep.
I followed David's suggestions and got the internal SD card out, created an image from it, copied it to the new SD card and after replacing the card, my device was brought back to life! Yay!
I also considered putting a fresh image onto the new card, but yet wanted to try use my old system (well all the stats were there and pictures drawn by my daughter - that I really wanted to get back
) while keeping the option of a fresh image in case when the old one would turn out to be corrupted or unusable any other way.
Well eventually I was successful with bringing back the old data from old SD card. Therefore I want to thank David for the clues and suggestions in this thread. They are really very professional and work like a charm
Thx!