regime on "Getting many "cannot modify header information " warnings"

Hi ,
I am really in trouble right now ! I keep on getting many errors of this type
Warning: Cannot modify header information - headers already sent by (output started at /usr/share/php/header.php:2) in /home/reg001/public_html/wp-load.php on line 64

first when i was installing wordpress it showed warning -
Warning: Cannot modify header information - headers already sent by (output started at /usr/share/php/header.php:2) in /home/reg001/public_html/wp-load.php on line 64

i saw the code for load.php file and saw the line of code executes if the config file does not exists . so i manually made config file .then this error went away !

But after that when i went to install i was getting a warning but i ignored it and registered admin . but now when i try to login admin is see -

Warning: Cannot modify header information - headers already sent by (output started at /usr/share/php/header.php:2) in /home/reg001/public_html/wp-login.php on line 390

Warning: Cannot modify header information - headers already sent by (output started at /usr/share/php/header.php:2) in /home/reg001/public_html/wp-login.php on line 403
shop

This is when i am using 4.5.2 when i was using 4.5.3 i was getting more errors.
My host is 5gbfree.com ! I dont know what the problem is as i had created another website a month ago and its working perfectly ( on the same 5gbfree.com host) (current address - http://www.reg001.5gbfree.com)
PLEASE HELP !! (I HAVE A DEADLINE TO COMPLETE WORK)