Now check for your files in Pen Drive.
format kr ke v dubara fer file paun te oh eda hi ho jndiya vaformat kar k v eda hunda a?
ohde pc ne saddiya pendrives da tn koonda kr taohde pc wich Virus hai
ask him to use NOD32 or Quick heal
and format your pen drive and change it from FAT to FAT32 or NTFS