If you have a problem with your database, change your password or delete and create it and try again.
The free hosting server might be abuse at a certain point and it might not be available from time to time.
Notes:
+ You have to create the database using MySQL icon before you can use it
+ It might take a little time from the time you create until it is available, please make sure you check using PHPMyAdmimn first before you try to configure it with your application.
+ Your config should point to MySQL hostname with 'mysqlXX.000webhost.com' format.
+ 000webhost version of PHPMyAdmimn is connected using 'sqlXX.000webhost.com' format.
Please check Mysql icon in your CPanel for more connection detail
Note: Remote Mysql is not allowed on 000webhost free hosting,