I have been confronted with the same problem, so I went to :
/xampp/phpmyadmin/config.inc.php
I pasted the password which I had enter earlier then I was able to access phpmyadmin again, there in the privileges tab/ edit/ I chose no password and go then it all came back to life 🙂
Also you can change the user to admin but your phpmyadmin would be in admin side and your other localhost website will not work either.