I have a problem with my Hard Drive and need to erase and reformat. Problem is my DVD drive does not work. Using Disk Utility and another Mac, I made a bootable USB and a DMG file of my original Snow Leopard install disc. Before erasing my HD, I tried to see if it would work. I booted off the USB and tried it. When I clicked on the "Install Mac OS X" icon, I got a message saying "TO install Mac OS X, use disc utility to burn this disc to a DVD and run this application again" What did I do wrong?