Yesterday I bought a Sony Memory Stick Pro Duo for my PSP. I brought it home and put 4 GB of videos in it. But when I put the memory in my PSP, the files were vanished! I re-inserted it to my PC and saw that although it was showing 3.98 GB used out of 15.4 GB, there weren't any file inside the memory. I tried all un-hiding tricks(through file explorer,CMD etc.) but literally there weren't any file inside the memory but the space was being used. I formatted it properly but the problem wasn't solved.