i installed this hack but my forum not openning now

here is the error i get while opening my webpage now:
Warning: require_once(/home/farsgsmc/public_html/includes/class_xperience.php) [function.require-once]: failed to open stream: No such file or directory in /includes/functions.php(1003) : eval()'d code on line 4
Fatal error: require_once() [function.require]: Failed opening required '/home/farsgsmc/public_html/includes/class_xperience.php' (include_path='.:/usr/lib/php:/usr/local/lib/php') in /home/farsgsmc/public_html/includes/functions.php(1003) : eval()'d code on line 4
please help me quickly