Please help! my phone got stuck on huawei logo at start up screen.

My p9 is L19 version running Marshmallow, and I want to upgrade it to Nougat but I confused to download firmware for rolling back from Nougat to Marshmallow that actually It's already running Marshmallow. After success After reboot it got stuck on Huawei Logo. I can't even turn it off or enter recovery mode. After ran out of battery It also got charging problem. Please help me. Thanks for your help!