Not powering on after teardown

Hi

So my friend gave me his iPhone 5s to take a look at, after he'd smashed it into the ground pretty bad. The back was dented and the top glass was shattered. After he'd dropped it, it had started acting strange like displaying an inconsistent and inaccurate time, not sleeping when the power button was pressed and the touch Id being really unreliable. I assumed it was a logic board issue, and when I removed the board I saw the logic board shield had been dented, confirming what I had assumed. I removed the smashed top glass panel and replaced all the components and the screen. When I tried to boot it back on, the phone wouldn't power on. Also, the flex cable between the home button and it's socket had torn too meaning I would have to replace the home button as well. The question is why isn't it getting power any more and what should I do about the faulty board.