Cannot get to dashboard

The problem is here:

wp-config.php:88

See: https://codex.www.ads-software.com/FAQ_Troubleshooting#How_do_I_solve_the_Headers_already_sent_warning_problem.3F

I’m getting over my head pretty quickly but have checked wp-config.php for the errors mentioned and they do not appear, ie:

Line 1
<?php

Last line
?>

The uploaded file date is 4 years old, so it hasn’t been altered.

Can you point me to what I should look at next?

Try deactivating all plugins – if you can’t access the Dashboard, use FTP or Cpanel to rename the plugins folder:

wp-content
     plugins.HOLD

Via FTP have renamed the plugin folder to
/www/blog/wp-content/plugins/index1.php

but still get the same error message when I try to access the blog dashboard.

(From memeory it’s pretty simple, Askimet and not much else)

What should I try next?