[Resolved] WordPress - Error in DataBase Connection or Access denied for user@'localhost' ?

Situation:

Website migrated from one host to another using UpDraft. Admin able to login on WordPress dashboard.

Homepage/ FrontEnd shows, Connection Error! Access denied for user@localhost.

What I did?

changed wp-config.php
after hours of meddling around and changing multiple times username and password on wp-config.php which shows DataBase connection error.
Optimized and repair DataBase didn't help.

What Resolved?

*Disabled the all plugin and activate one by one. *

Hosting Provider: HostGator