My phone won't turn on, whats wrong?

A year ago, my phone was cracked and stopped working and I tore the phone apart. I recently got energetic and put the phone back together. The screen worked and I could tell the phone was on. I ordered a replacement screen and after replacing it, the phone worked! I had charged the phone to 2% and figured I would charge it later when I got into class. The phone died, and ever sense then has not been working. I double checked the cables to make sure the screen was in right and everything was fine. It was. I don't even get a vibration when I plug it in to charge, or even if I try to turn it on.

What could possibly be my problem?

Also, the phone connects to itunes and I've tried the hard reset, recovery mode, etc. Nothing seems to work!