Motherboard just stopped working, completely after assembly!

Hi I was fixing my friends ipod 4th gen cracked screen and it was working before after first assembly and now it just completely stopped working after reassembly after digitizer didn't work, this is third time. I am at the end of my ropes, I have know how idea what I did to do this I was following ifixit. Please help, it was working. It started after first assembly now nothing after second, digitizer didn't work so i didn't again. I left for a bit after the first repair, left it plugged in and charging. But i don't have time so i was going way to fast. Did I short the circuit board? I don't know what I did.