Hello! I'm trying to install Mavericks in an old MBP 15" 2007 in which I have a Snow Leopard OS. I'm trying to do it from a bootable USB disk but I'm getting nowhere. I've done this exact same installation with the same USB device with 2 other different MBP 15" 2007 and it has work perfectly. Now, when I reboot the system and press the option key it recognizes the disk from which I have the Mavericks install software with zero problems, but then I choose the USB bootable disk so I would give the option to install and it boots directly to the snow leopard desktop like a regular boot. I've tried change the OS to another USB device, repair permissions and other minor stuff, but I don't know what to do next. Any suggestions? Thanks!