If on EBay you may have bought a "fake" one that's been changed to lie about it's size. Google "EBay Fake Flash".
If you bought in Best Buy or another large retailer, then your next step is to check with Photo Rec, Recuva, and Test Disk.
I have a USB drive (thumb drive) that I keep photos on. It has 5 folders that contained anywhere from a few dozen to almost 10,000 photos. The largest folder (that had contained almost 10,000 photos) now contains less than 1000. I don't know what happened to them. Right clicking on the drive and selecting "Properties" shows a pie chart that indicates the amount of space used on the drive hasn't changed so it looks like the photos are still there but I just can't see them. Any ideas? Virus? Any help would be appreciated! Thank you!

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