Hi, your "root" password should just be the same as your user's password by default. The prompt doesn't really want a root password, it wants an administrator's password, like yours, which gives you the same privileges as you would have as root. If you want a real root account, run mintAssistant and select enable, it should prompt for a password.
If you have a question that has been answered and solved, then please edit your original post and put a [SOLVED] at the end of your subject header
Hint - use a google search including the search term site:forums.linuxmint.com