I have 3 different USB external hard drives, the Maxtor that I use for backup and 2 Hitachi drives for working files. After I installed the Win 10 Anniversary install, the 3 external drives don't show up in File Explorer. All other USB devices still show up and work. The 3 drives still works on my other PC with Win 7.
When I open Disk Management I can see the Maxtor, but is unallocated. When I click Properties, it says the drive is working properly and the best driver is already installed. I went to the Seagate site to see if there was a better driver and could find one.
The 2 Hitachi's don't show up in the Disk Manager.