Have you changed your domain admin password? if yes go to epo....../core/config and put the new password and confirm. then restart the data base and epo services and try again
As per the error message the authentication is failing to reach DB... and also it could be port issue..
compare the port number is same from sql configuration manager for respective instance name and check the db.properties has the similar port specified.
I suggest to change to sql authentication, with simple user name and password and re-authenticate in core/config with this new user and do the test connection and click on apply and restart epo services.
Additionally: Attached the document with screenshots for the steps to follow