I have an old mac that I'm trying to fix. The model is Imac 24 inch from early 2009. I made a bootable external device with the latest capable software for that model. Right after powering on the mac, I press the option key which leads me to the choice of booting from that external device. after choosing the external booting device, the mac shows an apple logo with a loading bar (without booting chime) underneath, but when it reaches the end, it jumps to a prohibited sign. The mac It is connected to the internet, recovery mode doesn't work. What am I doing wrong?