Install MacOS from USB

https://support.apple.com/zh-hk/HT201372

Restart your Mac in safe mode and then restart normally. Doing so may help you fix your slow startup problem because safe mode performs a check of your startup disk. Here is how:

  • Turn off your Mac
  • Turn on your Mac and immediately press and enter the Shift key
  • Keep holding the Shift key until you see the login screen
  • Login (you may have to log in a few times)
  • Now your computer is in safe mode.
  • Then exit safe mode by restarting your Mac normally without pressing the Shift key.

Reset PRAM (or NVRAM). Here is how:

  • Turn off your Mac
  • Turn on your Mac and immediately enter the Option, Command, P, and R keys
  • Keep holding the keys for about 20 seconds
  • And then release the keys and your computer will restart.