The control panel will not load.
TRY THE ALTERNATIVES
Through the Client Area: Services > My Services > Login to cPanel. This signs you in without a password and works even if the domain is not resolving.
Directly: yourdomain.com/cpanel, or the server hostname from your welcome email.
IF IT LOADS BUT REJECTS YOUR PASSWORD
Reset it from the Client Area service page.
Note that resetting the cPanel password may reset associated database passwords depending on the options chosen.
IF NOTHING LOADS
Test from mobile data. If it works there, your address is blocked by the firewall.
Check whether the domain resolves. If not, use the server hostname instead.
Check whether the account is suspended. Client Area > Services > My Services.
Check Client Area > Network Issues for a posted incident.
IF YOU ARE REDIRECTED TO A LOGIN LOOP
Clear cookies for the domain, or use a private browsing window.
THE MOST RELIABLE ROUTE
Always the Client Area. It does not depend on your domain resolving or on remembering the password.