Help. WordPress gone haywire

I’ve had my wordpress site for 5 months and everything was fine. Today, I go to my site and see this in my header and footer. I can’t even log-in to my admin dashboard because it’s there too:

Warning: session_start() [function.session-start]: open(/var/chroot/home/content/30/7811030/tmp/sess_vqeq249p2d03scsqqc0db6nb11, O_RDWR) failed: File too large (27) in /home/content/30/7811030/html/wp-content/themes/mk4/functions.php on line 10

Warning: session_start() [function.session-start]: Cannot send session cookie - headers already sent by (output started at /home/content/30/7811030/html/wp-content/themes/mk4/functions.php:10) in /home/content/30/7811030/html/wp-content/themes/mk4/functions.php on line 10

Warning: session_start() [function.session-start]: Cannot send session cache limiter - headers already sent (output started at /home/content/30/7811030/html/wp-content/themes/mk4/functions.php:10) in /home/content/30/7811030/html/wp-content/themes/mk4/functions.php on line 10

What is this? How can it be fixed? Help!