There are several routes back in depending on what is wrong. All of them need cPanel access, so start there.
You have forgotten the password
Use the Lost Password link first. If the site cannot send email – a common problem in itself – you can change the password directly in the database. In cPanel open phpMyAdmin, find the wp_users table, edit your row, and set user_pass using the MD5 function from the dropdown. WordPress will upgrade the hash to a modern one the first time you log in.
The email address is wrong or unreachable
Change user_email in the same table, then use Lost Password normally.
A plugin is blocking you
Security plugins lock people out with some enthusiasm. Rename the plugin's folder in wp-content/plugins to disable it, log in, and adjust its settings before renaming the folder back.
Your IP address has been blocked
If wp-admin, cPanel and webmail all stop working at once while the site is fine for other people, the block is at the server rather than in WordPress. See Why we block IP addresses, and how to get unblocked.
A redirect loop
Usually the Site Address and WordPress Address disagreeing with how the site is actually reached – www against non-www, or http against https. Set both explicitly in wp-config.php:
define( 'WP_HOME', 'https://www.example.com' ); define( 'WP_SITEURL', 'https://www.example.com' );
These override the database and will break the loop. Remove them once the settings are corrected.
Your role has been changed
If you can log in but see almost nothing, your account may no longer be an administrator. That is worth treating as a possible compromise – see My website has been hacked.
