Have you installed MySQL server successfully? Did you run the MySQL instance config wizard? This is the utility you should run immediately after installing MySQL on a pc to configure it. In here is where you set the root password. The default user for MySQL should always be root, and whatever you enter for the password should be the password for the root user.
If you did not create a password you may want to try leaving it blank with the root username to see if that gets you in. Also you may want to check to see if you have a firewall or other security software that is blocking the port, I think the default port is 3306.