iPhone 8 Plus boot loop

Just replaced my iPhone 8 Plus back housing, since the old one has crack. Now that the phone is fully assembled, it boot loops. Apple logo starts to appear then turns off and then turns on again (looping). I tried to reseat all of the cables that connects to the phone, but still the same issue.

• What troubleshooting steps can I try to fix it?
• What could I have damaged if it keeps boot looping?