Not sure if you've covered this, but its from their website
The camera will not record video.
Check the memory card to make sure the locking tab on the side of the SD card is not in the ‘locked’ position.
If the card is unlocked, there is most likely a compatibility issue with the SD card. First, please try reformatting the card using the delete all function in the setting menu. If that doesn’t help, then please try out a different SD card. SD card performance varies widely between brands and class ratings. We recommend sticking to name brand SD cards with a class 4 rating or higher. We mostly use the Kingston and Patriot class 4 cards without any issue, so can safely recommend those.
http://gopro.com/support/troubleshooting-tips-hd/