That's exactly what should have happened!!
You hadn't previously set a password, and phpMyAdmin 'knew' that the password didn't exist (or was an empty string) so could get in.
Now you have set the Admin root password, phpMyAdmin doesn't know how to get in, until you tell it, which you would do in wampp or xampp or your phpmyadmin folder, (in Wampp it's: C:\wamp\apps\phpmyadmin18.104.22.168\config.inc.php) open the file 'config.inc.php' and enter the password that you have just assigned to your mySql database, in the line:
$cfg['Servers'][$i]['user'] = 'root'; /* 'Root' is the default username, and you should leave this as it is */
$cfg['Servers'][$i]['password'] = ''; /* Enter your password between the two inverted commas */
PhpMy Admin now knows how to get in, and so will PowerStore 3, with: