Database error occurred.

Are the db credentials properly set in /application/config/database.php? Does that mysql user have proper permissions set up? According to the error message, you are trying to use the "root" mysql user with NO password.

Finaly i can access database, but i got new error,

A Database Error Occurred
Error Number: 1146
Table 'cpp_db.UI_USERS' doesn't exist
select SALT as RESULT from UI_USERS where USERNAME='admin'
Filename: helpers/system_helper.php
Line Number: 153

I open file helpers/system_helper.php and i change all UI_USERS to lowercase because in my database all table is in lowercase, after i changed it nothing happen still same error.

by the way thanks for your answer. i appreciate it.