My presumption is that you are running on an MS Windows OS. With Windows, it sounds like you MAY have a corrupted FAT File:
1. Do NOT defrag your Hard Drive
2. Do NOT write anything to your Hard Drive.
3. If you have an undelete program installed -- Use it!
4. If you have different partition or Hard Drive, install an undelete program and use it. (For examples: www.undelete.com, www.winundelete.com, www.pctools.com.)

Note that you may not be able to undelete the directory, per se. However, the directory does not "physically contain" your "lost" files, it simply "points" to where they are. Hopefully, it is JUST the "pointers" that have been "lost."

LESSON LEARNED(?) == ALWAYS BACKUP IMPORTANT FILES.