I can't start using my Jiajyu G5

I didn't use my phone for the last 1year. I was off it and put it. And now I wanted to use it, but it can charge, and show the % and the light on and the phone name Jiayu came on the screen . But it won't start up won't off. I must to take it out the battery to off it. Otherwise I can't off it by pressing the power button.

I tried to start up by pressing the power button and volume down holding for 30 sec. and more. I tried that many times but it won't help.

I tried that I don't know what else to do.

That's why I came to you.

I hope my question is clear.

Please, stop asking useless questions if you can just try to help me!