How to remove raw file system from pen drive

It is ready for putting in the bin and replacing with a new one when you get errors regarding corruption etc. Pen drives are manufactured in their millions every month and are "throwaway" items when thay start giving trouble. Never save valuable files on them because their reliability is very low (especially the cheap ones with odd names).

Based on your description, your drive may be corrupted. What you need to is to apply a recovery program for reaching your inner files again and format it for saving the drive itself.
You should google “free recovery program” on the internet, for I know there is a free recovery program, which I have tried to restore my inaccessible data from the corrupted drive, just like you.
Note for you:
1. Stop using this drive immediately to avoid overwriting the original data, which can make your data gone permanently.
2. Save your recovered files on a different storage device in case of recovery failure.
3. Do not forget to format your drive to see whether it will work again.
4. Back up you data in the future in case of similar problem.