Why did all my PDF files vanish from my Kindle?

The first time I showed my Kindle DX to some friends, someone had done something similar to what you describe and it baffled me for a day or two. In fact, I started tweeting that I'd found a bug in the Kindle operating system when in fact what I'd found instead was a flaw in the user interface, the user experience of the Kindle reader.

To see what I mean, let me show you the oh-so-subtle way you can fix the problem and restore all the mysteriously missing Kindle materials -- and PDF files -- on your DX.

You need to pay attention to what's at the top of the screen on your Kindle. Here's what you're probably seeing (more or less):

What you need to do is use the little pointer gizmo to move the selector underliner to highlight that very top line that says "Showing 8 Books". Then this happens:

Notice the left and right arrows? Ahhhh, that's the secret! Click left on the pointer gizmo (what is that thing called?) and you'll find the secret revealed:

There ya go. The Kindle categorizes your information by category and somehow you've changed it to show you one particular category rather than everything. What I suggest instead is to select "All My Items". Now when you move back to your Home screen, notice on the top line that it's not quite the same:

So there ya go, the mystery of the missing Kindle DX files is neatly solved. Looking for more Kindle help? Well, heck, click on that and you'll find you've got everything ya need right here.