You may have encountered problems before if you tried running Disk First Aid at this point. If you're reading this, it's likely that Disk First Aid failed, and you probably saw some error messages that provided more questions than answers. What you may need at this point is a program that can look directly at the contents of the drive at a low level, reading blocks on the disk without using the I/O processes used by the OS X operating system.
After all, the OS can't read what we know is on the drive, and the OS disk repair software has failed. The utility programs that work here use direct access and block reading methods to read the data from the drive and reconstruct the file, folder, volume, and partition data that is present, but which has problems being interpreted by the OS.