Please check your phone for any of the following situations, and refer to the corresponding solution:
Scenario 1.
Complete black screen, and when pressing the power button, the phone will vibrate.
If the device is under such situation, suggest to apply for the after-sales services.
Scenario 2.
Complete black screen, and when pressing the power button, the phone won't vibrate.
If this happens, firstly charge the phone for 15 minutes at least and then try to turn on the phone again. If the phone has a black screen after powering-on, suggest you to apply for the after-sales services.
Scenario 3.
Occasional black screen, Please restart the phone. If it is because an app fails to open or displays a black screen after powering-on, uninstall the app and check whether the problem is solved.
Besides,you can also upgrade it to the latest stable version.
If the problem persists, contact OnePlus Customer Service for assistance.