z101 on 08 June 2015
Seems your USB stick is broken. It is very unlikely that you can recover its data.
Don't know which stick you are using but its always better to spend a little bit more money on USB sticks if they should hold important data.
Some cheap sticks are fakes: For example a stick will be sold as 32GB but has only 16GB in real. The stick controller fakes the data so it seems for PCs (or other devices like Wii U) that it is a 32GB stick. But when the 16GB are full it overwrites old data or gets corrupted.
