Power button not working after screen replacement

I've replaced the screen on a customers p20 lite using genuine parts. Everything seemed to go well but the phone will not power on. I assumed it was because of a low battery so I plugged it in to charge and the screen woke showing a battery charging screen. I left it to charge from 10% to 60% but it still won't power on. Whilst in this charging mode the power button will not wake the screen but the volume button do. I assumed the power button was damaged and replaced it but the same happens. Any ideas what this could be? Thanks