Why do I keep getting this error why I try to open this php file?

Database Error

There was an error connecting to the database.

The database must be installed as described in the appendix.

MySQL must be running as described in chapter 1.

Error message: SQLSTATE[HY000] [1045] Access denied for user 'mgs_user'@'localhost' (using password: YES)

I have the Apache, MySQL servers and PHP interpreter installed on my system. I can see from the XAMMP control panel that both servers have a status of running. Also, I can access and log into the phpMyAdmin tool. There aren't any port conflicts so I'm not sure what the problem is.