Tara on "404 error on every page"

404 indicates failure to communicate with the server.
- it could be configuration issue
- it could be memory issue
- it could be permalinks issue, try reviewing this: How to fix 404 error when using Pretty Permalinks?
- it could be optimization issue
- it could be a conflict with plugin: try resetting the plugin folder
- it could be a conflict with theme: try switching to the default theme for a moment via FTP and see if that resolves the issue.
- check for .htaccess file presence and check if the default wordpress mod-rewrite code is there or not. There are times when .htaccess file is not writeable or gotten deleted
- Check the server error log for your hosting account for any specific error message. Ask your webhost for assistance to locate them.