Computer Can't Read USB

Diagnostic

The computer can't read it either

Two minutes, in order:

If it offers to format or initialise the drive, say NO. Formatting now can wipe out files that are still recoverable.

Is this a Windows machine? Players read HFS+, the Mac file system, and a Windows machine may show an HFS+ drive as empty or not at all. If Windows offers to format it, say no, and try a Mac before you believe the drive is gone.
Plug direct, not through a hub or a dock. Bus-powered hubs drop marginal drives.
Try another computer if one is nearby. A phone adapter can prove the drive is alive, but the rebuild needs a computer.

Can any device see the USB now?

You follow these steps at your own risk. Full disclaimer.