Mysql problem

Hi im having this error when im trying to install the system...
Anybody who can help... i have tried to find some help here in the forum.. did not find any...

Please help..
what can i do?
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Pre-install validation

Setup has carried out a number of checks to see if everything’s ready to start the setup.

Checking PHP version: OK!

Checking if sessions are properly configured: OK!

Checking if assets/cache directory exists: OK!

Checking if assets/cache directory is writable: OK!

Checking if assets/cache/siteCache.idx.php file is writable: OK!

Checking if assets/cache/sitePublishing.idx.php file is writable: OK!

Checking if assets/images directory exists: OK!

Checking if assets/images directory is writable: OK!

Checking if assets/export directory exists: OK!

Checking if assets/export directory is writable: OK!

Checking if manager/includes/config.inc.php exists and is writable: OK!

Creating connection to the database: OK!
Database could not be selected!

Please check the database permissions for the specified user and try again.

Checking table prefix `modx_`: Failed! - Table prefix does not exist in this database!

Setup couldn’t install into the selected database, as it does not contain existing tables with the prefix you specified to be upgraded. Please choose an existing table prefix, and run Setup again.

Unfortunately, Setup cannot continue at the moment, due to the above 2 errors. Please correct the errors, and try again. If you need help figuring out how to fix the problems, visit the Operation MODx Forums.

The MySQL user you are specifying apparently does not have permission to use the database you’ve created for MODx (or you haven’t created a database and the user you specified doesn’t have permission to create a database).