Really, there are only 3 things that can go wrong.
1) SD Card needs formatting in the device you are using it in, as already suggested.
2) You must seriously check that you are using the correct SD card for your Device i.e. SD, HD, Super HD & so on. They simply will not behave when trying to cross them.
3) Buy another I'm afraid (as suggested), SD Cards are not the most reliable storage in the world and if it has been used in another device, it may not allow you to use it in any other, I have come across this problem personally.
I bought a brand new 32 GB SD card for my Kodak digital camera. It's never been used but won't work in my camera. Am I suppose to do something to it before I use it?
I have the same issue, my brother thinks that because the new cards are so large, my old camera doesn't understand it-I am taking the second one 16 gb card back and seeing if I can find a lower gb one.