Unable activate wp installation

I am totally stuck ….any help would be greatly appreciated.
I am using FileZilla and Plesk to upload and install the current version of WordPress on to my new domain. I need to intall WordPress first to that I can then add the Market e-commerce theme.

I have my data base configured and have the correct details in the wp-config.php file. I have uploaded the whole ‘wordpress’ folder to httpdocs which is the root directory. As per instructions in the forum and elsewhere, I deleted the index.html file in httpdocs to avoid confict. Maybe I should not have done this in hindsight????

When I then go to https://www.mysite.com/wordpress/wp-admin/install.php
I get the following error message

Error establishing a database connection
This either means that the username and password information in your wp-config.php file is incorrect or we can’t contact the database server at LocalMYSQLserver. This could mean your host’s database server is down.
?Are you sure you have the correct username and password?
?Are you sure that you have typed the correct hostname?
?Are you sure that the database server is running?

What am I doing wrong??