Panel phpmyadmin on my account doesn't work

Hello everybody! It's my first time here. I'm italian so sorry for my bad english. I hope somebody could help me.
I can't autenticate in myphpadmin on my account. The message say the credentials are incorrect. I have installed the 1 click cms and then cancelled it because I wanted to manage the site by ftp. Can it be the reason of the problem? Plus, I have on my homepage the 'site under costruction' message, I don't know why...