Need Fix For 500 Internal Server Error Logging on to Backend - Joomla! Forum - community, help and support

i in need of tech assistance. began getting 500 internal server error last saturday when logging on backend. not familiar enough issues relating problem. have tried .htaccess remedy , configuration.php no success. error logs state "premature end of script headers: index.php" on all. need help.

thanks in advance.

http://www.gsvaonline.org

joomla 1.5.21 (i know, need update this)