Problem with first login

I’ve just installed everything and on my first login I get

4 similar messages (all on the same page):

I then can’t go any further – any ideas anyone?

Warning: Cannot modify header information – headers already sent by (output started at /home/content/j/o/h/johnpea/html/blog/wp-config.php:23) in /home/content/j/o/h/johnpea/html/blog/wp-login.php on line 9

Warning: Cannot modify header information – headers already sent by (output started at /home/content/j/o/h/johnpea/html/blog/wp-config.php:23) in /home/content/j/o/h/johnpea/html/blog/wp-includes/pluggable-functions.php on line 274

Warning: Cannot modify header information – headers already sent by (output started at /home/content/j/o/h/johnpea/html/blog/wp-config.php:23) in /home/content/j/o/h/johnpea/html/blog/wp-includes/pluggable-functions.php on line 275

Warning: Cannot modify header information – headers already sent by (output started at /home/content/j/o/h/johnpea/html/blog/wp-config.php:23) in /home/content/j/o/h/johnpea/html/blog/wp-includes/pluggable-functions.php on line 247