Why is my phone stuck in a boot loop?

Hey everyone!

I’m having a problem with my iphone 6. I’ve recently replaced the screen and the battry and now my phone seems to be stuck in a boot loop.

I’ve read and tried a lot of things over the past few days. I currently have 3 screens and 2 batteries. I tried assembling a combination of all those parts to eliminate the problem and/or figure out what it is. As far as I’m concerned it’s not the battery or the screens. I’ve also checked if there is a problem with the individual screen cables(the camera, the lcd etc). But so far I haven’t come to a conclusion.

Do you have any suggestions? What could be causing this? How can I fix this?

PS. Restoring the phone using itunes also hasn’t worked. I keep getting the error code as the phone keeps getting in the boot loop and itunes can’t proceed with the restoration.

Thank you all in advance!