Warning: Cannot modify header information - headers already sent by [no duplicate]

Warning: Cannot modify header information - headers already sent by [no
duplicate]

hi in my website i am having this message on every page.
and i am not able to open my admin panel now.
http://www.alexandrasplayground.org/wp-admin/
Warning: Cannot modify header information - headers already sent by
(output started at /home/alexan/public_html/index.php:218) in
/home/alexan/public_html/wp-content/plugins/wp-super-cache/wp-cache-phase2.php
on line 90
i tried to remove plugin from cpanel and tried to reload website but still
not able to load admin panel.
please help me in this.
my wp-config look like this.
please help me where to update?