WordPress 404 Fix & Update

I’m facing a site-wide 404 error on my WordPress installation. I’ve already tried resetting the permalinks, but every page—homepage included—still throws the error. Because the site runs on both a custom theme and several bespoke plugins, I need a careful, code-safe solution.

Here’s what I’d like you to handle:

– Diagnose and eliminate the 404 issue (checking .htaccess, database rewrites, plugin or theme conflicts—whatever is required).
– Bring WordPress core up to the latest stable release and confirm the update doesn’t break the custom theme or plugins.
– Test the full site after the fix so every URL loads normally and all custom functionality works as before.
– Provide a brief change log and any recommendations for future maintenance.

I’ll supply full cPanel and WordPress admin access along with a recent backup. Once the pages load without errors and WordPress is fully updated and stable, the job is complete.