This is absolutely frustrating. I have changed my password on my main x10hosting account and can get onto EVERYTHING else BUT CPanel. Are the passwords not the same? What is going on!?
The passwords are not automatically (though you can set them to be) the same. Same goes for user name, in your case your forum name (which is what you use to login to your account panel at x10hosting.com/panel.php) is not the same as you should use for cPanel.
In your account panel you have the option to change cPanel password. Your cPanel user name is: mcternan