If you bookmark your cPanel when you're in it, your browser stores the address you're currently using. Occasionally, when we upgrade the cPanel software such as when we did from cPanel version 10 to version 11, this address changes. In the case of the v10 to v11 upgrade, the 'theme' which makes cPanel look pretty changed from the 'x2' theme to 'x3'.
If you want to store a bookmark that is always going to work, even with upgrades, edit the bookmark to be http://www.yourdomain.com/cpanel/ replacing 'yourdomain.com' with your own site's address.