[wdhewitt]

Note4 is fully updated. Running Win10 on laptop. Connected by USB cable.
This setup worked fine for transferring files both ways.
But I messed it up trying to root the phone.
Unfortunately I can't find the notes for just what I changed.
When I plug the phone in I get the 'not recognized' messages and I can not see the phone in the Device Manager.
When I plug a USB drive directly into the phone I can not see the drive in X-plore.

The laptop recognizes a Neo5 and transfers correctly. The Neo5 also recognizes the directly plugged in USB drive so it is definitely a Note4 issue.

[Rukbat]

First, plugging a USB drive into the phone won't let the phone see the drive, you need an OTG cable (or adapter).

Second, if you can't remember what you changed, you may just have to reflash the firmware. Depending on the variant of Note 4 you have, you might be able to install TWRP without losing data, then you can back the data up. Otherwise, see Backing up an Android Device, back up everything, then reflash the firmware.

[wdhewitt]

Rukbat, Thanks for the advice. I won;t be able to try it for a bit due to travel but I will.

Regarding the OTG
I have a very neat Memorex 32GB drive which has a normal USB on one end and a Micro on the other end. When I plug it directly into the Samsung Neo 5 it is recognized as a drive. The Note 4 used to as well. I also have a very old Sandisk MicroMate SD-SDHC card adapter that works the same.