Cannot Modify Header Information 2.3

I am actually having a few problems with my WordPress Blog, but now it seems I can’t even log in to the WP-Admin anymore. I upgraded a couple of days ago and despite the other problems I could still login to the admin, but now I can’t even do that:

d [this same “d” appears on my actual blog page, where the theme has been erased and the “d” appears at the top. The “d” also appears throughout the main admin screen and the above the blue ribbon on the admin screen] Warning: Cannot modify header information – headers already sent by (output started at /home/bravenew/public_html/wp-config.php:25) in /home/bravenew/public_html/wp-includes/pluggable.php on line 390

The other problems listed are:

Also, to publish an entry I have to first click save or save and continue editing twice before I can publish directly. When I do click publish or save instead of saving the entry name it just says “”

Also I can no longer add my own categories, it used to say in a pink box that you have no permission, but now it says “d-1” in that pink box.

I also get several errors in reference to the database and lines of PHP files when I try to publish, activate or deactivate a plugin or theme after the upgrade.