ADE Refuses to Sync

I have version 4.5.10.186048 installed on my PC. I have about 100 ebooks - both epub and pdf format - in my library. The entire library refuses to sync. At some point, it synced with my Samsung Galaxy, but it's stopped. Only about half my books are there and the rest won't show up. As a test, last night I installed ADE on my ipad, and only 18 books synced to that device. 

I've already taken these steps:

• Made sure I was logged in on all devices
• Authorized/deauthorized the devices
• Checked for updates on every device & updated when necessary
• Started and closed the apps multiple times
• Refreshed multiple times
• Made sure that auto sync was turned on on all devices
• Made sure all devices were connected to the same wifi network

I spent hours on this last night am beyond frustrated. (And I only resorted to using the ADE app on the Galay because the ADE app on my PC has NEVER ONCE recognized the device, so I can't sync the books into my Nook library, which was what I really wanted to do. So this is a workaround that doesn't even work!!! )

I'd appreciate any help. Thank you!