Most Blu Ray Player are compatible with FAT23, FAT16, FAT32, no NTFS, so if you're using NTFS hard drive for Blu Ray Player, it won't recognize it. Reform partition in Windows system will loss data, your hard drive will become an empty disk, while you don't have another external hard drive for backup, format partition to FAT32 is not the best choice. Convert NTFS to FAT32 without losing data in Partition Expert is the best option.
Connect your hard drive to Blu Ray Player again, and you can access all of the folders. I have my hard drive tested in Sony Blu Ray Player, and it worked.
When Disk size is over 2TB, blu ray player can only recognize 2TB at most if you disk is MBR, leaving the rest of partition or space unreadable. In this situation, you can convert MBR to GPT in Partition Expert without data loss, so that the whole hard drive can be read in Blu ray player. Here're the steps to convert MBR to GPT
Connect the USB flash drive, or external hard drive to Blu ray player, see the result.
Another thing should mention is that some hard drives are still not accessible even after you converted NTFS to FAT32, MBR to GPT, because hard drive size is getting larger and larger, from 500GB to 1TB, 2TB, 3TB, and even 4TB. We need to change cluster size when formatting, so that we can make full use hard drive capacity.
Steps to format hard to large cluster:
Now, we solved all the problems related to blu ray players won't recognize hard drive, do the above mentioned steps, and your hard drive will be recognized by blu ray players, no problem to access all folders.