We need more detailed information to figure out your problem.
If you receive the "not formatted error" message, as venspidia writes, you can try a memory card recovery freeware from http://blog4mark.blogspot.com/2013/01/memory-card-recov...
Even though I have never tried it, my friend has used it to recover all his data back after accidental format. That's why I recommend it to you.
Have a nice shot!