Session management on your server is not working correctly.
I uploaded a file named sessionTest.php to your server:
sessionTest.php
On clicking the second link, the session variables value is cleared, this should not happen.
you will need to contact your host to resolve the issue, most likely it is a problem with the php session.save_path setting.
It would also be a good idea to change your login details for fatcow and for PowerCMS