I have made a basic error, I have built an installer for an 18,3 machine and used it on a 12,2 machine. The result is that the install hangs after the second re-boot. I have built the correct installer and tried to run that but it still hangs after the second re-boot. Is there any way back as I now cannot boot any operating system on this machine. I don't want to format the machine as I will lose all my videos which are not backed up.