I recently was asked to help a friend that had shot about 30 photos of a wedding when her Sony camera suddenly reported "Bad format" or something like that and wouldn't let her take nor view photos. I inserted the memory card (Memory Stick Pro) into my computer and tried accessing it to check if the problem was the camera's fault. But no, Windows reported that the removable media was not formatted and offered me to format it.
I had read on several web pages that this type of problem is frequent and that there exists software to recover data in such situations. I started looking around the Internet for an alternative, preferably freeware, and ended up using this one: Free Art Plus Digital Photo Recovery. The program was able to recover all photos on the memory card, however two of them had errors in them.
I highly recommend this software and suggest you download a copy and store it on your USB drive or something. It does not require any installation, is completely free and is virus and spyware free.