Administration access lost.
WHAT TO ESTABLISH
Is the password wrong, or is the page failing?
FOR A WRONG PASSWORD
Use the reset function.
If the reset email does not arrive, that is a separate problem: mail delivery.
IF THE RESET EMAIL DOES NOT ARRIVE
Reset the password directly in the database, through phpMyAdmin.
Or create a new administrator account there.
FOR A REDIRECT LOOP AT LOGIN
Usually the site address settings, or a plugin.
Rename the plugins directory to test.
FOR A PAGE THAT WILL NOT LOAD AT ALL
Treat it as a white page or 500 error: check the log.
IF YOU ARE LOCKED OUT BY FAILED ATTEMPTS
A security plugin or the server may have blocked your address.
Check from mobile data. If it works, that confirms it.
IF AN ADMINISTRATOR ACCOUNT VANISHED
That is a serious indicator. Treat it as a possible compromise.
WHAT TO DO AFTERWARDS
Set a strong unique password Enable two-factor authentication
