Is your cPanel page opening? if Yes Please make sure your login details are correct.
or No then Did you change DNS for your domain name to our hosting ones?
Did you change default cPanel password that you received in your hosting welcome email?
if No Please refer to welcome email for your hosting account for correct login details.
We advise you to copy/paste the information from welcome email to avoid any mistyping. Make sure you do not have any additional spaces before or after login and password.
If you didn't receive welcome email, please contact our hosting support team via live chat (skype id - hostholder.com) or ticket system and you will be assisted.
or
Your cPanel can easily be accessed through your Client Area->Services.
Simply click on the cPanel button next to the domain you would like to access and a new window or tab should pop up in which you should automatically be logged in cPanel.