Open a command prompt with administrator rights and enter the following sequence of commands:
diskpart
list disk
select disk {number}
clean
create partition primary
select partition 1
active
format fs=fat32 quick
assign
exit
In the "select disk" command, replace {number} with the drive number of your USB drive as indicated when you ran the "list disk" command. Check and double check you choose the correct number since this procedure erases everything on the drive you select.
Or download UNetbootin
