I use PostNuke myself, ever since the PHP-Nuke developer freaked after some big exploit and completely changed his distribution system, but what you may want to try is to delete or recreate the databases, since this is a new install. Go to the install.php to do this. After that, you should have a fresh database without an admin user, and you should be able to set the password. If not, then you might want to checkout your database, find the DATABASE.nuke_users table, and examine the first or second entry. They list users, and the first should be guest or anonymous. The second should be your admin account. Note that the password is hashed so you can't figure out what it is by looking at it, but maybe if you either a) deleted that user and then try to click on make a super user account, or b) cleared the field for the password hash, you might be able to log in with no password. At the very least, you would get the name of the Super User.

Good luck.

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