I held down COMMAND + R, went to Disk Utilities and unmounted then erased the harddrive. Then I went to reinstall mac os. It was on El Capitan. It asks me to connect to WiFi, I do. Then after a few clicks it asks to login Apple ID. After I try to do that, it says This Item is Temporarily Unavailable. Please try later. I tried later, a few hours later, even a few days later. Gives me same message. How can I reinstall MacOS? I have a USB flash drive with Lion installed. When I try to boot from USB by holding Option during a power on, it comes up with a message my computer must be restarted. Hold the power button til it turns off, then immediately press the power button again. I've tried doing it a few times. It gives the same error message. I know the flash drive works because after that I used it on a different one to reinstall.