After upgrading from 10.3.9 to 10.5 Leopard my mac will not boot from the hardrive even after I set up the hard drive as the boot disk after the upgrade. The mac will start to boot but then cut itself off. I have to leave the 10.5 disk in the drive and hold down C and that will only allow me to install the 10.5 software again. How can I force my mac to boot from the hard drive?