How do I get the device to power back on?

I received it when it was still powered on and the Taptic was still functioning but once it turned off it never came back on even after charging it. I deemed its original battery inoperable and replaced it along with the screen since it’s original is cracked (I still have the screen). I swapped all I needed and put everything in order but it still won’t turn on or even vibrate. I put it on to charge and it got really warm. But no signs of life. The brackets that go over the battery and screen connectors were missing when I opened it up.