iPhone 6 wont turn on after battery and screen replacement

I bought a new lcd/digitizer and battery from amazon for my iPhone 6.

I started by turning off the device and opening the phone. I disconnected the battery and proceed to take the screen off. I made sure each screw was in the right place so I don't mix them up. I replaced the battery first and did not connect the battery yet. I then transferred all the original cables and metal back piece including the home button/digitizer onto the new screen. I put everything back together and connected the battery and closed everything up.

Now the phone wont turn on. I have tried connecting the phone through a laptop to see if it would read but no luck. I have switched everything back to the original screen and battery but still no luck.

I tested the battery and the voltage is 2.5, working normally I supposed. I then tested with charger connected to see if current was flowing and it was reading under 0.4.

In conclusion based on my research online could it be the U2 or IC chip that needs to be replaced? Any input would help.

Thank you!