The FMU on Pixhawk 2.4.8 not working

Dear Friends, I need some help!
Today, I run the motor without propeller to check the battery life (few day ago, my drone was still working), after 4min, the motor stop and the main led is off. The FMU power led is still on but B/E is off, I can’t connect pixhawk to Mission planner too. I open it, there no damage on the board, no smell too.
Do this problem may solve? Please guide me. Thanks for reading!