I doubt that it's formatted as NTFS. NTFS is not really designed for removable drives and Windows warns you about that if you try to force an NTFS format on a removable device.
The most likely issue is the file format. The players I've used won't even list files in an unknown format. Also, you're right, HDTracks does not sell copyright-protected files although you might still run into some purchased from iTunes.
The most likely issue is the file format. The players I've used won't even list files in an unknown format. Also, you're right, HDTracks does not sell copyright-protected files although you might still run into some purchased from iTunes.