Did this happen after updating Win 8 to 8.1? That happened to me, and it turns out that the 8.1 installer arbitarily chages the graphics driver to a generic driver of questionable value. All I knew was that Photoshop slowed dramatically after updating to Win8.1 and low and behold, GPU acceleration was greyed out.
In my case a visit to the nVidia drivers site fixed the problem.
No, I've been using win 8.1 all along and it worked fine at first. One day the OS just froze though, forcing me to do a forced reset (pressing the power button). I don't really know if that was the cause, but it's one of the only 'major' things that happened that could've possibly caused the problem. That, or a win8.1 update.
I have just tried fixing registries too, but to no avail. I tried updating nvidia to the newest version, rollbacking and updating again, but I have actually yet to reinstall nvidia. I guess I'm going to do that now...
Edit: I missed some lines on the sniffer_gpu.exe output
OpenGL ok, version 1.1 CUDA 4.2.1
Return code: 3
That does indicate that your video driver has a bug.
Have you contacted NVidia about this?