Samsung Galaxy S5 (VZW) is totally unresponsive

Phone LCD does not light up. If there *IS* an image, I can't see it.

Phone does not vibrate.

It does not make a sound.

No LEDs light up.

The Menu and Back buttons do not light up.

I do see cracks on the glass, but they are actually on the underside of the glass. The Home button is wobbly and on one end, flush with the glass.

I have used micro-USB cables, but not micro-USB3 cables. I have charged the original and an aftermarket battery in an external charger. I have plugged the phone into a Windows laptop with a regular micro-USB cable. The phone remains unresponsive.

The worse part? Apparently, someone's done work on this phone - the home button is black. The glass (and midframe) are white. Yuk.

Assuming no liquid damage, where should focus my efforts for an effective repair strategy? I'm aware the power IC is a BGA, but I don't how the phone behaves when this IC does bad.

TIA for your feedback.