Hi again, my problem got miraculously solved. That is, after having started win4lin successfully (to my surprise) all other programs start again. But I don't have any explanation for that 27 hour spell of my machine, and how to prevent future happenings of this kind.
So, if you happen to be a Linux or Debian guru or for some other reason have some idea on that: I still would be interested in how to investigate such an occurrence. Andreas Goesele
