Instead of using the cpanel ssh interface, do you have any software for ssh connections?
If you dont then try to download bitvise tunnelier, and then connect to your account using the same username and password of your cpanel, of course you must first ask support to enable ssh on your account, please when you do that explain why you need ssh enabled.
Depending on the server your site is located the ssh port will be different, so be sure support tells you which port you must use. (download)