1.
Databases and users are started with your account user name, so a db named database1 would be called user_database1, and the user name would be user_databaseusername...
I have done this item correctly at the time of install.
2.
You should always be able to access a database if you are the user...the user is added to the database in the cpanel mysql options, not from phpmyadmin.
The cpanel mysql option was the method that I used to setup the original databases. I only went to phpmyadmin only after I wasn't able to access the database. This is the place where I only imported the records from the old database to the new database.
3.
Have you called/emailed the host? Did they upgrade the database versions?
I have not done this yet but did find this notice from the knowledge desk regarding this matter:
Warning: mysql_connect() [function.mysql-connect]: Access denied for user 'someone'@'localhost' (using password: YES) in /home/cpusername/public_html/config.php on line 3
Couldn't connect to server.
This error tells you the exact situation. "Access denied" is your big clue! This means that the database user or password is incorrect in your php file. The database name must always be cpanelusername_databaseusername. You can check the correct spelling in cPanel, under MySQL Databases.
This seemed to answer the initial problem until I checked the database in cPanel and found that the user name was spelled correct. Thinking that the password may have been wrong I verified what was stored in the database file and it only displayed the admin password which was spelled correctly.
Any further assistance will be appreciated.