1.    Find and right-click the Windows Command Prompt in your Start Menu and choose to run it as an Administrator.
 
2.    At the prompt, enter "diskpart" to launch Microsoft’s disk management utility. The command line should now read “DISKPART>”.
 
3.    Type "list disk" to show a list of all disk drives. If your USB key is plugged into your PC, it should be listed here, along
 with other physical drives. Note the USB key’s disk number – you can pick it out by looking at the disk capacity.
 
4.    Type **"select disk #", with the USB key’s disk number in place of #.
 
5.    Type "clean" for the utility to clean the disk, which DiskPart will confirm.
 
6.    Create a new bootable partition by entering "create partition primary". 

7.    Choose this partition with select partition 1, and then mark it as active by typing "active".  

8.    Format the key by inputting "format fs=fat32". This should take a few minutes, and DiskPart will display a progress percentage. 

9.    Lastly, type "assign" to give this USB key a drive letter. Close the DiskPart program using "exit"