Many PHP and Perl scripts use a default host name localhost. If your PHP or Perl configuration files require a host name, be sure to use the host name mysql, not the default host name localhost.
Next check to see that you are using the correct user name and password combination. You must create a user name and password when setting up your database; you'll need this user name and password anytime you want to access your MySQL database. Learn more.
If you're still seeing a problem, make sure that you have not initiated a database backup, database restoration, or database repair. If you have initiated any of these actions, your database will become inaccessible until the operation is complete. To view your database status, click the "MySQL Database" link on the Create & Update tab of your Web Hosting Control Panel, then click the "Database Status" link.
If you have deleted the user yroot from your MySQL database or changed the password for this user, you will no longer be able to access your database. Your database will need to be reset.
Finally make sure that you have not exceeded your total disk space quota. If you exceed the disk space available in your plan, your database scripts will no longer function on your web site, and you will not be able to access your database. To solve this problem, you can either delete enough files to bring your account below your disk space limit or change your plan to one wiht more disk space. Once you are below your limit, database access will be restored. Compare the Yahoo! Web Hosting Basic, Advanced, and Premier Plans.
Please note that you can access your database using either PHP or Perl scripts run from your web site or the phpMyAdmin database management tool. You can create custom scripts or install publicly available packages that use a MySQL database, such as our advanced add-ons. You will not be able to access your database using a desktop client or other tools run outside of Yahoo!