Thank you for such a detailed anwer. I wonder why the device shows "software missing" of "system software missing" but it's probably not that important. The device indeed stays in preboot mode during this text but when i click OK in updater.exe i get:
Spoiler: Click for Image
[Only registered and activated users can see links. ]

after clicking OK the unit turns off. I can turn it on again but i see no change.

Anyway, thanks again. It really looks like the hardware fault. I think i'll just look for motherboard or something if I want to revive it