I just want to share my experience of multipleGPU in windows 7. I'm not sure if it is the case always, but in my case, it is so.
To make two GPUs work ( I have two 5970s, thus to make the first one of each work) , I must connect both GPUs with a monitor, then restart my system, after restart, I must remove the connector of monitor of the second GPU, then GPU and GPU will work, while GPU and GPU is still not working due to internal crossfire.
Am I right? At least it is the case in my system. Why has anyone never told me this?