Once in your lifetime, when you insert a SD card (or other alike storage devices), you'll see this dreadful thing:
No fear, just never click on "format" and you'll be fine. Open a Command Propt and simply type in this simple command line and return:
Note the "G" is the drive name you saw in the first photo. After just 1 second or 2, you'll see the command output and, bingo, your drive's content will pop up as it usually did:
If above not successful, you can try TestDisk. But be sure to do above first, because it is a 100% recovery and the process takes no time. With other methods, you'll usually lose at least the original file names and they may take several hours to achieve only a partial recovery.