Screen does not work after replacement

Hi, seems like something went wrong… I followed all the instructions, but at the end of the reassembly, the phone does not turn on. I plugged in the charger and pressed the power button, but there is only a slight vibration, the back/home buttons light up, and then nothing. The device repeats this every few seconds. I tried power + vol down for a few seconds too, LED goes red and then same result (repeat vibration + back/home lights blink). What’s the problem here? What might I have missed? Is the new display or new battery faulty?