Why won't my iPhone turn on?

Previously I asked a question concerning replacing the screen and LCD on my iPhone. I had leaned into something with no actual impact, just pressure from me leaning, and when I looked at my phone the screen was black. I came home and replaced the screen with the old screen that was previously broken (the LCD still worked when I bought the new screen, but my current screen was cracked real bad which is why i bought a new one) but that screen would only light up long enough to show a few white lines on a black screen. So it was suggested to me that I get a new screen before deciding how much damage was done to the phone. I now have a working screen, but my phone won’t turn on! I toggled the vibrating button to see if it was on and that maybe I yet again put on a faulty LCD, but alas, no vibration. I also tried to hold the power button for about 15 seconds. It wasn’t plugged in for several days, but now it’s been charging for 3 hours. At the time that I leaned into something and the screen cracked, the phone was still on. It would also still vibrate when I toggled the ringer. I had to finally use muscle memory and turn the phone off because the back light was staying on but the screen was black. Since the phone was staying on after my accident I thought having a new screen would fix all my problems.. Is there anything else I could try or should I just leave it to the professionals?