No problem at all. So the only thing I need to be aware of is that I have to enable USB file storage option in the firmware settings by going to firmware settings via web browser (default ip address like 192.168.1.1 etc). Once that setting is enabled, I simply have to connect any USB storage to the router and it shows up as a network location in windows. Can also access it using and iPad through the Documents by Readdle app. As simple as that.
If the drive shows up empty, like in your case, I'm not sure what the problem. Maybe try reformatting the drive to fat32 or exfat or ntfs, and see which one works? If that doesn't solve it, then try connecting some other USB drives to see if those work