Sounds familiar... the reason could be Win7 plus newer drivers.
Here is a shorter version based on
this post how to get most cards working at once:
- Install Win8
- or, if applicable: Wipe any old drivers off with amd_cleanup_util_1.2.1.0.exe (google)
- Install drivers 13.1 plus OpenCL included with it
* You may now have 5 GPUs working with one with an error code 43 inside the Device Manager.
- Open Drivers 12.6 and install only to the point where it extracts stuff into C:\AMD\Support\. Do not actually install drivers. We just need to extract.
- In device manager, on the card with the "!" manually install the extracted driver from C:\AMD\Support\12-6_vista_win7_64_dd_ccc_whql\Packages\Drivers\Display\W76A_INF
* It should now proceed to downgrade from 13.1 to 12.6, which is the highest version driver that allows an extra GPU.
Note: You screen may flicker MANY times, and your device manager may appear to freeze/hang. Just let it do it's thing. It may take upwards of an hour or longer. You may get a BSOD too. Just go with it. If you're coming on 2 hours or longer, try doing a hard reset. You -should- now have all 6 GPU installed OK in device manager and detected in OpenCL. If not, reboot again (just in case).
