My MacBook Air of 7 years won’t open anymore. When I open it, it shows a file with a question mark (?) and only after I reboot it and restart it a couple of times it will finally open after a very long wait. I can’t reset it to fabric settings as I’ve seen it’s recommended to do, because the hard disk isn’t showing up when I want to erase the things on it, neither I can install a new OS. Any idea if I can fix this problem and how? Mention that I can’t afford to take my Mac to the service right now, so any tip would be highly appreciated. Thank you!