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Perhaps you have access to the database. Go to it through MyAdmin. Search your account - for example through a search. In the table "users" go to edit. Check your group and set there in groups - 1 (administrator / webmaster). If you have changed your password in the field "password", change the password for the new - here you have left the field type and select MD5. That should do the trick.
PS if you have the correct permissions for the files? Primarily for mainfile.php?
I recommend immediately change the password for the database - so sure.