Error Establishing A Database Connection is very common error we get sometimes while running our website. WordPress get this error when it has problem in accessing database.
1. Can be an issue in wp-config.php file i.e by mistake we entered wrong database details there.
2. Database alloted quota is limited and our site has crossed that limit.
3. Webserver is down.
How to remove error:
1. If problem is with wp-config.php file, then locate the file though ftp and recheck all details about database(database name, username, password and database host).
2.If error is in quota or if webserver is down ,than contact web hosts for the solution.