Cannot Modify Headers Issue Results in Inability To Log In

Hi!
I am having an issue with my website, http://www.TurningHeadsKennel.com
normally, to log into wordpress I visit: http://www.Turningheadskennel.com/wp-admin
But I get an error page. I'm not all that tech savy and am not sure how to get things back up and running or why there appears to be a conflict. Any help or tips to get me in the right direction would be greatly appreciated!

Thanks & Happy New Year