hello, what is your firmware version? you can try to enter the factory mode to reset your phone / here is the guide link : viewtopic.php?f=192&t=334922
I do not know what firmware.Fon is blackview s8 android 7.0 I tried to flash with S8 ROM but it can not. He can not guess mtk preloader driver..The service can not do it. Fon not boot with buttons.