Can anybody help with this, please?
I copy books via USB into the Documents folder on my Kindle Paperwhite, but recently when navigating on the Kindle they are not appearing in the list of books in my Library, so I can't view them.
(I've restarted the Kindle, removed and reloaded the books & changed settings all to no avail).

[CaptainKidd]

What is the file extension of the books you are trying to load?

Kindle Paperwhite supports the following:
AZW is the Kindle format, note that some files might have a number, such as 1, 2, or 3, after the AZW. I have never had trouble by converting files to AZW3 prior to direct loading onto my kindle in the manner you describe.
MOBI, a file format developed by Mobipocket, is widely used and compatible with the Kindle Paperwhite. Note However; secure Mobipocket or secure MOBI files do not work on a Kindle Paperwhite. (again, see comment above regarding AZW3)
PRC is equivalent to MOBI and is the standard file format for the Kindle family of e-readers for content that comes from sources other than Amazon.com.
TXT is a simple text file, such as one you might create with Notepad.
PDF: Kindle Paperwhite can display files in Adobe’s Portable Document Format (PDF).

Hope this helps, Good Luck!!

I tend to convert DRM removed .epub to .mobi then copy them into the Documents folder & not normally had any problems. I've Reset my Paperwhite back to factory settings and I'm reloading it with books. The only thing I could think of is that I've copied over folders within folders and thats cause problems, so I'm trying to avpoid doing that and see if that works. Many thanks for your reply.

But can I ask what you mean by "secure mobi files" as I'm not sure what that means (DRM'd files?) As far I can see I've always removed the DRM from books I've bought and those I get from Mobilism I convert to epub using Calibre.
Cheers & Thanks again