I was away from my computer for most of the morning and just saw all of the emails about the site being down. After a quick investigation, I found that some of the database tables required to run the site were corrupted. This was causing the home page to show up incorrectly, and the pricing page would show the book detail but wouldn’t display any prices on it. The problem has been fixed now. I’m still trying to determine the cause, but it will likely just be ‘one of those things’ that computers sometimes do. Thanks to everybody who sent me an email letting me know about the problem.