It would appear so. When I rename the directory that contains all the actual eBook files Calibre starts up normally, whether or not the computer has been rebooted since the last use of the program. In the process of starting up, it creates a new, empty eBook directory.

Does this suggest that perhaps a file in the eBook directory is corrupted and causing the delay? The directory tree is: D:\Library\eBooks\[Author name]\[Book Title]\cover.jpg, and [title.mobi] and metadata.opf. The title.mobi file is the actual eBook.

Since this eBook library is four or five yeas old (or older?) and is added to weekly, if there is a corrupted file I should be able to find it by sorting by date modified and moving newer directories out of Calibre's search path until Calibre works normally again. Remember, everything worked right until just a few weeks ago, nothing changed except the addition of new eBooks to the library.

I do not allow iTunes anywhere near my computer, thanks to your pointing me towards "CopyTrans Manager" several years ago. (Couldn't you use CopyTrans to back up your iPhone?) I ran the APPWIZ.CPl, and there is no Bonjour. I also did a search for "Bonjour" on my C: drive just to be sure, and the program is definitely not there.

I have Adobe Acrobat 9, plus Adobe Reader in my computer. They have been there for years, carried over from my Vista system into my 8.1 system and now into my Windows 10 system, and they have co-existed with Calibre during all that time. There is no atmfd.dll file anywhere on my hard drive.

Since, as Mr. Goyal said, something must have changed in my system to cause the problem, I can only think of two things that are different: A Windows 10 update, or the addition of a new, corrupted eBook file. The second option seems the most likely.

Or am I looking entirely in the wrong direction? The fact that the program loads normally with an empty eBooks directory, but loads slowly when the directory is populated, is suggestive.

tanstaafl.