You might find a better response going directly to an nvidia forum as these issues are largely unknown and unsolved without tech know of the actual components I guess. My best advice is to run a few benchmarks OC and downclock, reinstall drivers using a sweeper and if all else fails reinstall...
i have heard that in order for crossfire to successfully work you need at least a x4 slot. I think that x1 slot is coking the bandwidth and causing it not to function.
I had the same issue and what fixed it was seperate updating of the drivers or using driver sweeper so that both cards are using the same 'version' drivers. If you look at gpu-z you can see if this is what is causing the issue. As I said, it was the same for me.
I have a similar setup to you using 2x 5870 on a 750W psu. I had probs and concluded that 850Watts would be better. On my current setup at 750W I can everything to work except heaven benchmark which shows only gpu 1 working in afterburner. CCC shows that crossfire is linked and on, but that. SO :)
I can think of two things that you can try to see if it fixes it?
Check your video cable and if it's pretty standard then consider upgrading to a gold plated HDMI or HDMI to DVI adapter also with gold plating. Also a shorter cable can reduce latency to your screen which you should also...
After watching this YouTuber Vid I am now considering that we should be worried and LHC. To recap what I believe is that this Norway spiral was created by the LHC like a by product as an example. Also time travel can occur when you bend light in a spiral which I saw in another youtube vid, but...
I use an online blog to communicate with family interstate. If I ever want an online service like cloud to prject a "new" business I would definitely consider it. :)
Personally I would have hated my music being pwned globally by some junkies high aspirations to rip off the industry and charge people to listen to invariable recordings of music he never knew existed.
Stuff Piracy.