Check the following:

• Is the Rechargeable Li-ion Battery installed?
  Is the AC Adapter connected to the printer?
  If not, install the Rechargeable Li-ion Battery or connect the AC Adapter to the printer.
   
• Is the USB Type-C® AC Adapter connected to the printer without the Rechargeable Li-ion Battery being installed?
  Because the USB Type-C AC Adapter is used only for charging the Rechargeable Li-ion Battery, the printer does not turn on or print without the battery being installed. 
  Make sure the Rechargeable Li-ion Battery is installed before turning the printer on.
   
• Is the remaining charge in the Rechargeable Li-ion Battery low?
  If the remaining charge is low, charge the Rechargeable Li-ion Battery.

If the problem continues, contact Brother customer service.