Sorry, I do not have a video on how to check the error logs, but this is something that the system administrator who installed your AtoM instance should know how to do based on the documentation links provided in my last message.
I recommend that you forward my last message to whoever installed and currently maintains your AtoM installation and ask them to answer all the questions with as much detail as possible and return the full error message from the logs. Otherwise, there are dozens of reasons why your site might not be working - and all of them will require access to the back end to fix anyway.
We will still need this info to be able to help you further!