The right answer was switch 1 and 4 on the Dip Switch to on and then to off again. Unfortunately this isn´t mentioned in the manual. Got the tip in the Usenet.

I bought a used Siemens D 1107 Mainboard and received it without the Bios Password. Is there any chance to get a Master Password or to corrupt the bios, that it opens.
The problems is that I don´t even get to the DOS Prompt.