Make sure that caps lock is off, and that you are completely sure what your cPanel password is. If you are trying to copy/paste a password, make sure you are not copying any empty spaces. If too many failed login attempts are made, you will be locked out of the system for 10 minutes. If you try to login during the 10 minute lockout period, the lockout will be extended.
If you cannot remember your cPanel password, it can be reset by using the link on the cPanel login page which appears if you make a mistake (the new password will go to the contact email address we have on record for the account). Or you can submit a Support Ticket for assistance.