Nano4 won't talk to PC

HI Folks,

Failing to download files from a Nano4 - I have searched back through the forum and found some similar threads but no solution. When I connect my Nano4 to a PC, it turns on, but the PC doesn't see it (in some cases it recognizes there is a USB device attached, but can't see any file or folder structure). I have tried the following:

1. Resetting the Nano.
2. Attaching the Nano in both power on and power off state
3. Multiple different USB cables
4. Two different PCs and both Windows and Mac OS's.

I have also tried emailing files from the Nano to myself (presumably via the LXNav server) but it can't get access, although it connects happily to Wifi.

Any thoughts?

Thanks,
Jon