Maybe this is any help for your issues? From Rockbox Wiki
Formatting a Player that cannot get past the Database Refresh in the OF
If you damage the filesystem on the internal SD you can find yourself in a situation where the database refresh in the OF hangs up and you will be unable to boot into the OF and also unable to connect via usb to correct the problem. If you find yourself in this situation 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. This will bring you into the normal top menu in the OF and you can then format your player through the settings menu.