Mac Start Folder Question Mark Solution:
If you see a blinking question mark on the Mac screen at startup, it means that your Mac cannot find its own system software.
If the flickering question mark on the Mac only shows for a short time and then continues to boot, you may need to re-select your boot disk in System Preferences.
Select “System Preferences Settings” from the Apple menu, and then click “Start Disk”.
Click on the disk icon that you normally use to boot your computer. Usually called “Macintosh HD”.
Close the System Preferences window.
The Mac should now be able to start properly without flashing question marks.