Please tell me how to use MySQL with the root user.

I got err: 1045. u know what, i could get in my PHPMyAdmin once, user name, "root", with no password and i could use it. but after i made a new database name and password, and log out, and never again to enter. i tried n tried, also with cmd, but useless. i wanna go on for my project but now i feel like a disaster. sb, help me with this, i beg.