A theme can cause fatal errors, blank pages, layout failures, or missing functionality when its code is incompatible with WordPress, PHP, or a plugin.
- Check the debug/error log for files inside the active theme.
- If wp-admin works, switch temporarily to a current default or known-good theme.
- If wp-admin does not work, rename the active theme directory only when another usable theme is installed and a backup exists.
- Retest the failing page with plugins unchanged so the theme is the only variable.
- Restore or update the theme only after confirming compatibility.
Do not delete the only available theme while diagnosing a production site.
