If you get the error "#1045 - Access denied for user '<yourusername>'@'localhost' (using password: YES)" then there is an error with either the username or password you are using.
In most cases it will be a password error.
Try changing the password for the database you are attempting to access via the Control Panel and attempt to log in again. You can change the password for your MySQL Database user without knowing the original password.
For PHP applications (PHPMyAdmin is one of them!), restrict your password characters to upper & lower case letters, and numbers. PHP applications sometimes use "escape" certain characters, so it is often best to avoid anything except letters and numbers.
It is important that your password is as strong as possible.