only stays on when plugged in and vibrator not working

I just recently replaced the front display and after i tried turning on the device and i noticed no matter how much i held the button it wouldn't turn on. So naturally i plugged it in and the screen popped up with the apple logo and it said it had 100% battery and as soon as i took it off the charger it went dead, won't turn on, nothin! Also i noticed the vibrator doesn't work anyone know what happened? thanks!