Partitioned a space in my external hdd and restore the mavericks here to create a bootable disk. At start-up I press and hold "alt" button and then see the bootable disk, select it but nothing happens and existing leopard system boots normally. I know it is not possible to install mavericks over leopard. But at least I want to reach to the installation screen and here delete the leopard and make a clean mavericks setup but I can't even reach that screen. What might be wrong ?