Original post by: Dan A+ ,
Have you tried booting from a DVD drive that you can attach to your Mac via USB? They sell these types of DVD drives at Walmart and Best Buy, among other stores. If that doesn’t work, then the problem may be with the Mac installation itself. Try reinstalling a new copy of the macOS and starting over. Turn on the Mac and press and hold '''command +r''' until you see the Apple logo. This will launch macOS recovery, and “Reinstall macOS” will be one of the options.