Why will my phone won't turn on or screen stay black

Began having trouble with what I thought was the on button not turning on my xt1650-1 phone. Repeating attempts we're usually successful until eventually it would not turn on at all. Plugged into charger the battery charge level was inconsistent but it then would show 100% charged . Screen glass was already cracked and online solutions suggested the led digitizer was bad. I replaced that and the battery and it still will not turn on. It does vibrate shortly after plugging into charger. Could the on off cable be damaged?