P9 lite cannot boot up only show device is booting

Hi Masters,

Need your advice here.

My p9 lite cannot boot up and only shows your device is booting now screen.

I cannot power off even force power off, and there is no responding whatever key combinations i pushed.

The step taken to this error is I did unlock my p9 lite and tried to flash twrp by following the guide, then I cannot enter fastboot mode and recovery mode after that.

I tried take out the battery and let the phone disconnect with power supply, after i put back the battery, i push the power key it still shows same screen as your device is booting now.

Any idea how to resolve this? I assume some fatal error with the motherboard, but i can say nothing after i unlock the phone.

Your suggestion and advice are much appreciate！ thank you!