I have a MacBook Air 2013 with macOS Sierra 10.12.6 installed. When I press the power button, the flashing folder with question mark appears.
I've started Internet Recovery (in the startup disk selection screen the internal disk is also missing) and with Disk Utility I ran 'Repair disk' / 'Repair volume' multiple times without any errors.
I can mount the disk and navigate through all my stuff in the terminal. I've booted from an external disk (also 10.12.6) and I can open any file from the Finder.
I've also tried resetting both the NVRAM and SMC to no avail. Booting into Safe Mode doesn't work and I can't reinstall macOS on this internal partition.
How can I troubleshoot this further?