Why Doesen't My Phone Turn On?!

Why Isn't It Turning On?

So I had this weird thing that even when my phone was charging it STILL won't turn on.

I tried things like hard reset, soft reset and etc. and it stopped working for 2 months from now on. I even followed stuff on YouTube and yeah, IT STILL DIDN'T WORK.

So is it just about the battery or the phone?

Please help me...