Could not connect to the database server at 'localhost' with the supplied username and password. Are you sure the hostname and user details are correct?
For that you need to create a database in your Cpanel
and need to create one user in cpanel
Both will be done in Database section (I don't remeber the exact name for where it will be done ) but for sure in Database section the first option
and Assing it to a user and give all the privilleges
Thans which ever username password you are using for user that you need to put where it ask for username and password when installing
That is odd. Try using the database name and password for the username/password.
Edit: Did you get a default database when you signed up? Sometimes they send you the details via email etc.
Woops sorry about that I forgot, well still some hosting companies send a default name and password when you sign up with them. But it's very odd you can't create a new user.