Solution:
In your situation it is very hard to pinpoint what’s wrong with your website but you can try narrow down the source of the error.
Possible causes:
There might be a corrupted file somewhere in your WordPress core or broken theme or badly coded plugin that mess up your database.
Backup first:
Nevertheless try backing up all your WordPress files including the database before doing anything else.
Reinstall:
Once you have your backup delete whatever files you have and reinstall your site bit by bit to troubleshoot the issue. This will also ensure you have a clean WordPress core files.
- Install a fresh copy of WordPress with default theme and database installed.
- Once done upload your theme and activate it and make sure the site is showing up just fine.
- Followed by upload folders and plugins. Reactivate the plugins and check the site again.
- Lastly replace your database file and check the site, if there is no error that means the error should be somewhere in your core or the templates. If there are errors then the errors most likely originated from your database.