How to tell if motherboard or screen problem

I dropped my Nexus 6 on the floor the other day, the top left corner glass is chipped, but no additional damage. Screen won't turn on. Plugging into power warms up the phone., so at least the battery charges... Phone was on silent/DND before, so is there a way to tell if the motherboard was damaged or just the screen/digitizer? I don't remember the phone ever vibrating on startup (during the Google screen).

I popped open the back, the power/volume buttons cable had popped out of its socket at the top corner I put it back. Still no power to screen, removed screws and battery tray, made sure all other cables to between motherboard and display were secured.

Should I just go ahead and ebay a screen unit and replace the screen to see if it was that, or does this sound like an issue with the mobo?