Totally beautiful. Finally I got all 4 cores to work properly. I cannot hardly understand it. I've used countless hours trying to make it work! But I never give up! And it pays in the end!
Now I have all 4 cores working just beautifully, giving between 325-330Mhash/s each at 800Mhz clock.
Here is the command for the 4th GPU:
phoenix -u http://firstname.lastname@example.org
:email@example.com:8332 -k poclbm DEVICE=3 WORKSIZE=256 VECTORS AGGRESSION=11 -v BFI_INT
I fixed this remotely through software only (tightvnc connection).
I am running driver version 11.5 for the 5970 card (downloaded from ati page), and the ATI Stream SDK 2.4. I installed the driver first, then I installed the SDK after. I also went into ccc and unticked all boxes in the settings (sorry for the poor explanation, but I can't be bothered to fire up ccc again over the slow vnc connection to check which boxes I unticked.).
However I think it is the driver version and ATI Stream SDK version that fixed the problem. Once I saw that the GPU started working a little, I figured it was just a software problem. I thank everyone for trying to help me. And everything is now solved, alas nobody in particular helped me find the solution that worked, that I did find myself, so the bounty will be saved for now.
But if you are running a dual 5970 rig under windows 7, 64 bit, know it is possible to make it work, even without a crossfire cable. Hope this thread also helped somebody else but me!
Thanks again everybody, and have a great day! I am a happy man now!
allinvain: thanks for your suggestions, yes i do use phoenix as you see.