A USB flash drives stores all the data in its memory similar to a hard drive. The operating system can later on fetch this data when required to be accessed. There can be various issues that may turn your USB drive data inaccessible such as if the drive is uncounted improperly from the port then it can lead to data Corruption. Another reason for the stored data corruption can be invalid data in the Master Boot Record (MBR) or Partition Boot Record (PBR) or directory structure on the USB drive.