My lovely Cowon D2 decided to greet me with a 70ies display of green and purple rectangles some days ago (read: b0rked). Switch on, boot screen – rectangles.
After some banging of head on walls I found this thread which guides one through the necessary steps to recover the player. Basically one needs to download the desired firmware version and use tcctool to upload three bin files contained in the firmware zip – 0 formats the internal flash memory, 1 is the firmware, and 2 contains fonts and graphics.
10 minutes later – I can has music to go again *yay*