Hi Steve, thanks for your response. When I enable wp_debug and wp_debug_log, an error message is displayed instead of the blank login page:
Warning: Cannot modify header information – headers already sent by (output started at /hermes/bosnaweb27a/b806/nf.xxxx/public_html/blog/wp-content/themes/ifeature/inc/admin-about.php:1) in /hermes/bosnaweb27a/b806/nf.xxx/public_html/blog/wp-includes/pluggable.php on line 1210