When you completed the one-click installation of WordPress, you should have received an email from the "One-click installation robot", that had instructions in it. Can you locate that?
When you completed the install, a password was assigned for the "admin" user, and a message on the screen told you to write that down, as you will need it to "log-in" for the first time. If you don't have that available, you will have to take another approach.
There are several methods you can use. First, go the the WordPress login page, and click the "Lost your password" link, enter "admin" for the user name, and instructions sahould be emailed to the email address you assigned to the admin user at install time. Other methods are described in the WordPress Codex article on "Resetting Your Password", though you may find some of those more difficult to follow.
Of course, you could delete the old installation, and re-install, but I'd try these things first!