how to make multiple gpu work?

Now I have 3*gtx-295. But I run the simplemultipleGPU in the NVIDIA SDK. It only shows 1 gpu. But if I enlable the SLI, it shows 4 not 6. Does anybody know what’s wrong?
Thank you very much!

I found a strange thing. If I connect 2 monitors to the computer, the program simplemultipleGPU shows 2. But if I connect only 1 monitors to it, it shows 1. But I connect 4 monitors to the computer, it shows 3 not 4.

I am guessing you are using either windows 7 or Vista, in which case it seems that you will want to read this thread. It seems interactions between Window WDDM and the NVIDIA driver makes enumerating GPUs in Vista/7 rather more complicated than in Linux or XP.

Which nVidia driver version are you running? Some older driver versions may still require “dummy plugs” connected to the VGA ports such that all GPUs are recognized.

The driver is 190.38. Now I have used the dummy plugs and enabled the quad sli. The program shows 5.