You can use Windows Diskpart to re-format a USB key and re-partition it.
Open a Command Window (cmd)
diskpart
list disk (it is important you KNOW which disk is the USB key you are formatting)
select disk x where x is your USB key.
clean
create part primary
select part 1
active
Open a Command Window (cmd)
diskpart
list disk (it is important you KNOW which disk is the USB key you are formatting)
select disk x where x is your USB key.
clean
create part primary
select part 1
active