I changed my iPhone 6 battery to a new one and not displaying again wh

Hello,

This could be caused by many things. I've seen many of these and the main causes are:

Not seating a connector properly

Bridging a contact/pin/connector

Incorrect cable placement

Failure to properly prepare the device for repair

Failure to ensure the device is off

All of the above are common causes of boot looping. Here are some troubleshooting steps:

1. Hold the home button and power button while on boot until the apple logo shows. Let go of the pwr (Power) button and hold the home button until it reaches a screen with: A computer, a website URL and a itunes logo. This is DFU mode (I think correct me if I am wrong)
2. Try reseating the internal connectors
3. Test on another iphone (If you have another one around)
4. Good luck!