Clip Zip - stuck on "Refreshing your media..."

[RufusA]

I recently took delivery of a mint condition used Sansa Clip Zip (which may have had latent issues)...

Player initially powered on, and I could navigate to Music, Video etc. without problem - though player had been wiped, so there was nothing to play.

Plugged player in to Win 10 PC, and player goes in to a boot loop i.e. Sansa flower animation, blank screen, Sansa flower animation, static flower for a minute, then repeat.....
In this state I can't connect to it, so can't flash new firmware, rockbox, or re-format.

Unplugging from PC, it gives me a "Refreshing your media" message, with the progress bar stuck at around 20% until I reset the player.

I have tried charging fully, draining fully, connecting with select button pressed, plugging / unplugging at various states of boot etc.

Is there anything else I can try, before I return to the seller as faulty? Is there any way of getting to the file system, or resetting to factory without successfully booting?

Thanks - Rufus.