Sony Xperia Z5 Premium that won't start up

? Need help here ?. I've got a Sony Xperia Z5 Premium that won't start up. I've tried holding in the power button along with the volume button and it doesn't even work. I've held it in for about 20-30 seconds and still nothing works. It's only vibrating but it won't display anything. What do I need to do? Does anybody know a solution that could maybe fix this issue?