Cannot login since update 4.2.1 – no login form just message

The front end of the site works but when i attempt to login i get the message below instead of the login form. Here is the site url

i’ve deactivated all plugins through the cPanel but the message still remains.
I’ve read numerous threads but can’t get it to work .

Any suggestions. Thanks

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Error creating a database connection
This either means that the username and password in your wp-config.php file is incorrect or we can not achieve on localhost database server. This could mean that the database server of your host is offline.

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Are you sure the username and password are correct?
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Are you sure you have typed the correct hostname?
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Are you sure that the database server is running?
If you do not know what it all means, you should probably contact your host. If you still need help you can always visit the WordPress Support Forums.