It's my daughter's Sansa Clip+ that has this problem - it's on Rockbox 3.13.
Booting up gets to the Rockbox splash screen, then "scanning disk" appears and stays visible. I've gathered that this could well be a sign of a corrupt file system and the solution is to reboot into the original firmware and fix it there, either over the USB or via reformatting.
But rebooting into the original firmware just gets to a 'Refreshing your media' progress bar which gets to 100%, and does nothing for several minutes before sometimes rebooting (into the original firmware, interestingly) and repeating the attempt to refresh.
So I'm left suspecting that there's a corruption in the directory structure, but I'm...
.. unable to get in via USB on Rockbox (no USB support on the Clip+)
.. unable to get past the "scanning disk" message
.. unable to get in via USB on the original firmware (no USB support until the refresh is finished)
.. unable to get past the refresh.
Is it stuffed?
If so, has anyone successfully returned as faulty a Clip+ that clearly tries to boot into Rockbox and has thus had its firmware played with?
And would it be a good idea to have some way to get past the "scanning disk" message? Something that goes 'Ah, I hope you have a backup because it looks like you need to reformat the flash and reinstall everything. I can do that...' would be very, very helpful at times like these.
Update: Ah ha! The "you can bypass the OF database refresh by connecting your player via usb and disconnecting it just after the Sandisk logo appears on the screen" method on the wiki has finally worked - it must be sensitive to when you unplug it.