Follow these instructions to reset Brother Printer:-
First of all, turn off your Brother Printer
Press and hold down the GO button
With the go button still held, turn on it back on again.
When the three lights light up, release the button and then press the go button TEN times.
Wait until the ready light is lit.
Your brother laser printer should now be factory reset, and all the error lights (toner, drum, and error) should have stopped flashing.