System is Arch Linux. NTFS-3G is installed. I have had this problem on Gnome (Nautilus) and KDE (Dolphin). I already tried fixing it with Testdisk. No success. Any help is appreciated.
UPDATE: I have re-formatted the disk and it is working now. Thank you for all your suggestions and tips.
At this point I will probably just back up all the files and re-format the disk, as I can mount usb flash drives without any issue, so I am assuming there is something wrong with the external hard drive.