Not much info here… Was your site working, fully set up and now is not?
Take a look at your WordPress config file, is it pointing to the database correctly? You would use FTP to get to that file.
To see what may be going on with your database, go into your DH panel. You can see the database name and current credentials there. You can access phpMyAdmin through the panel, too.
Was it just a temporary glitch, perhaps caused by traffic? Is it working now?
Try opening a ticket if everything looks right but is still not working.