Thanks, for your suggestions. I'm reasonable familiar with both the Controlroom and and the settings under the Devices menu, it was pretty much the same in Cubase 4. The problem is'nt to be found there so far I can tell.
Yet, Conman wrote the magic words "If your ASIO driver is correct". It seems that the the ASIO driver don't work as it should. The soundcard is visible in the Divice setup, its possible to route the "ins" and "outs" and change all the other settings, so it fooled me for a while. But by misstake I did start up the computer with the Mackie Onyx soundcard turned off so Windows choosed the soundcard on the motherboard instead. Suddenly Cubase behaved in a normal way on the screen. I have no speakers connected to that soundcard, so there was no sound, but I'm shure that it had worked. Still, the built in divice is'nt the soundcard of my choice, so I'm gonna try to get my old Mackie Onyx back in business. So far I haven't had any success, I have made a new installation of the drivers with no positive result, but I will go on trying.