After using my HD200 as mass storage device, I suddenly couldn't get in
contact with the device. When plugging in the USB nothing happened, and
if I started the player itself it would stall.

Using disc management (control panel - administration) in Windows, I
was able to see the hard drive, so I formatted the drive (FAT32). The
MPIO Utility software didn't work for me, so I downloaded the
archivefile for mac-computers on MPIOs homepage, unpacked it using
StuffIt (free download), transfered the folder (SYSTEM) and the file
therein to my HD200.

I started the HD200, which seemed to auto-create the standard folders
(MUSIC, FM, etc.). Now it is playing again!!! Great!

Hope some find this info useful.