go to the ISP who is hosting your site and make certain that you have adequate privileges. although in this case its "localhost". so its down to you or your developer.
the way MySQL security works is on a GRANT of privileges to specific users on specific machines or IP Addresses.
the error message you are getting could be
incorrect userid
incorrect hostname or IP addresss
or both.
so you need to either open a command line copy of MySQL and apply the
GRANT command
or
downlaod a copy of the MySQL GUI tools from their website and apply the privlieges from MySQL Administrator
if you do use the command line client then make certain you
MySQL FLUSH PRIVILEGES before leaving to make certain the server loads the new privileges otherwise it will continue with the old privileges until the server is restarted
MySQL :: MySQL 5.1 Reference Manual :: 5.5.2 Adding User Accounts