12-21-2014 09:59 AM
Ah, a clue! You mention that files can only be seen that were transferred from "this" computer. On the device, change the USB mode then reconnect. You will see the "phantom" music files.
Files transferred in MTP mode cannot be accessd while connected in MSC, and vice versa, due to the way the player's USB controller is set up. Simple solution, switch the USB mode as found on the device under Settings / System Serrtings / USB Mode.
After plugging in using the alternate mode, be sure to revert the device to the previous mode so you can access all of your music files.
The sample music tracks on the device are transferred using MTP mode (where the device is seen as a "media player". Many folks were puaaled when those sample tracks couldn't be accessed, if their computer was using MSC (where the device is seen as a basic storage device). If Auto Detect is selected, on some computers, it will flip to the alternate mode. Select the USB mode manually.