I have the exact same issues:
I was using my gopro hero 3 Black edition - got it for Christmas. Everything was fine once I had the right drivers on my PC (still using an XP). I used it last 3 weeks ago, then decided to use it yesterday for the first time. I charged the camera up - then turned it on, it gave me the NO SD error.
What I did: I took it out of the camera and put it into the card reader: it was like I had a blank card reader.
When I connect it via the camera, the computer says it needs to format it.
I tried formatting it via the camera, and after it formats it, it says SD error. BTW, lost a lot of good video too, that I viewed on my computer (so I knew there was stuff on it) but stupidly never transferred to my hard drive - thanks gopro or Sandisk: whomever is at fault here…
I tried formatting it via the camera, but on the computer (on both my XP and Windows 7 machine), and they both go through the formatting process only to say that it can’t format the card.
What is disturbing is that neither GoPro nor Sandisk are saying ANYTHING about this on their web sites: what is going on???