Need help for playback

Volumio is connected via Ethernet, control via PC connected to the same wifi network. I have a 1TB HD connected via USB directly to the modem.
when I select a track appears a circle that turns, turns, turns and nothing more.
My collection is about 600GB.
Volumio reads the .cue file, .ape?
The problem is repeated on flac and mp3 files also.
I cannot understand the problem…could you help me, please?
Thanks a lot

So you’ve attached a USB hard drive to your router? Can you access the files on a regular computer connected to the internal network?