Possibly unique twist on the 'Error establishing a database connection' message

??I can access my database fine using phpMyAdmin
? While index.php has that filename, I cannot access the front-end of the website —?I get the ‘Error establishing a database connection’ message
??However I can still login and access /wp-admin perfectly fine

? Note that I don’t use index.php in my URL or permalink structure
??If I rename index.php to index2.php for example
??And I accomodate that name change in the URL e.g. example.com/index2.php/blog
??Then I can view that page!

So, my wordpress install is able to make a datbase connection after all?

But not for the front end of the website when index.php has its original filename

The front-end of the website only works when I rename index.php

Could this be a database issue, a wp-config issue, an .htaccess issue?

Any help would be very much appreciated!

Many thanks,

Jamie