It would seem that either you are entering incorrect database user/password or that the database user specified does not have the required permissions. In either case, your hosting provider would be the right party to contact.
Do let me know if there is anything specific I could help with. Thanks.
Please PM me your CPanel (or whatever has been provided for managing the site) username and password. I'll see if I can find something. (it is quitting time for me right now so I'll only be able to do this when I get back. Hope that is OK with you). Thanks.
If you can access your site's phpMyAdmin, you'll see all the required info displayed in it. Alternatively, you can also ask your hosting provider to give you that info.