Open a Command Prompt window (cmd) with administrator authorizations.
Enter the following commands:
>DISKPART
>LIST DISK
>SELECT DISK X (donde x es el pendrive)
>CLEAN
>CREATRE PART PRIMARY
>ACTIVE
>ASSIGN LETTER X (donde X es una letra de unidad disponible)
>FORMAT FS=NTFS QUICK
>EXIT
Then copy all files on bootable USB.