Okay, It was completely dead and I tried everything. I left the battery out for a while (like 30 minutes) and when I put the battery back in the Nikia logo suddenly appeared! It went dark after that, but I could use the power button to switch it on again.

Then I switched it off, to test some more. Dead of course.

I strongly suspect that the device does not shut down properly and it has something to do with the software... If I have more news I will post it.