Hi there, there are sorts of solutions to fix the flashing question mark given by your Mac device when it loads up:
1. Check Startup Disk System Preferences
2. Reselect the right startup disk in macOS Recovery mode
3. Repair the startup disk or Macintosh HD with Disk Utility
4. Format startup disk via Disk Utility and reinstall macOS
5. Check and replace the startup disk (HDD) cable
6. Update the firmware of your MacBook
7. Check the lifeboat connector on the logic board
8. Check the faulty SSD socket or hard drive on the Mac logic board
Worthwhile, if you have any important files on the Mac computer, you'd better recover files before you fix the question mark appearing when your Mac starts up.
