I had a battery problem. I guess?

I don't know what should I start first.

One year ago, I bought galaxy s7 from Amazon.

Recently, my phone just shut down automatically even battery was fully charged.

So I decide to change the battery.

even I didn't connect a new battery to the phone

It shows like this and left side corner is getting hot even I didn't turn on the phone.

Also, I connect a new battery to the phone, It shows the same thing as I didn't connect.

After I changed battery, I charged battery fully, but when I disconnect from charger, it shuts down automatically as before then the battery is just starting to charge from 60%

What problem is this phone?

Which part should I change?