Thanks for your advise.
After removing one of the unnecessary plugin, following error has gone but still website is showing 404 error
Notice: Function wpdb::prepare was called?incorrectly. The query argument of wpdb::prepare() must have a placeholder. Please see?Debugging in WordPress?for more information. (This message was added in version 3.9.0.) in?/home/kzmyx2mxkvh4/public_html/wp-includes/functions.php?on line?6085
