Did you follow the step below after putting it back together? These laptops are particular when you pull the boards out and put them back in.
To avoid logic board damage, when your MacBook repair is complete but before powering it on, connect it to low-voltage power using a 5-Watt iPhone charger and a USB-C to USB-A cable. These accessories are not included with your MacBook, so make sure you have them ready before you begin