I can't go to any pages or links off of my Wordpress Dashboard. Comes back as 404: Page Not Found. I have tried everything to fix it

Question

I am in a bind. All of a sudden, when I log into Wordpress admin and go to the Dashboard, all other links from that page lead to 404: Page Not Found. I cannot go to settings, or pages, or posts, or anything. It loads the Dashboard just fine and the Frontend of my website is fully functional (www.wapsifly.net). I just can't change or add anything since I cannot access anything through Dashboard. I have turned on Debug and am showing no errors in the browser or in the log file. As far as I know, nothing was changed before we started having this problem. No plugins were added, removed, or updated. No changes were made on the server. I am really new to all of this, so please let me know if you need something more from me in order to help with this issue. I have now spent 2 full days trying to fix this. We are needing to update data on our site by Thursday, August 1, 2019, so I am running out of time. Any and all suggestions would be greatly appreciated.

What I have tried:

1. Manually resetting permalinks through FTP.
2. Disabling all Plugins by changing the name of the plugins folder in FTP.
3. Disabling custom theme through phpMyAdmin
4. Rebuilding .htaccess file
5. Manually adding site URL's to wp-config

This is the code I added to wp-config to turn on Debug:

// Enable Debug logging to the /wp-content/debug.log file
define( 'WP_DEBUG_LOG', true );

// Disable display of errors and warnings 
define( 'WP_DEBUG_DISPLAY', true );

// Force Display Errors even if disabled in php directive
@ini_set( 'display_errors', 1 );

// Use dev versions of core JS and CSS files (only needed if you are modifying these core files)
define( 'SCRIPT_DEBUG', true );

When I rebuilt my .htaccess file, this is all that was in it:

# BEGIN WordPress
<IfModule mod_rewrite.c>
RewriteEngine On
RewriteBase /
RewriteRule ^index\.php$ - [L]
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule . /index.php [L]
</IfModule>
# END WordPress

Answer 1

Try fixing your permalinks if you can access them.