Did you set your MySQL\phpMyAdmin password from the Security
menu link in the XAMPP Demo Page at http://localhost/index.php
If not then remove any changes you made in the config.inc.php file and go to the Security link and then set your passwords.
Select Cookie or http authentication instead of config.
See if there are any helpful posts in these advanced search results
This post from the many in the above search seems to have had a positive result even though it is a bit long winded:viewtopic.php?f=16&t=38844