I have just done a fresh install of PHP Nuke 7.4, the install files were downloaded straight from the main PHP Nuke site only a day or so ago.

I always get the following at the top of every page.

Warning: Cannot modify header information - headers already sent by (output started at /home/********/public_html/html/config.php:121) in /home/********/public_html/html/mainfile.php on line 162

I get the following at the top of the page when logging in as an administrator.

Warning: Cannot modify header information - headers already sent by (output started at /home/********/public_html/html/config.php:121) in /home/********/public_html/html/auth.php on line 46

I get the following when trying to log in as a regular user. All that is shown on screen here is a page with a white background and error #1 and the below two errors in black text.

Warning: Cannot modify header information - headers already sent by (output started at /home/********/public_html/html/config.php:121) in /home/********/public_html/html/modules/Your_Account/index.php on line 792

Warning: Cannot modify header information - headers already sent by (output started at /home/********/public_html/html/config.php:121) in /home/********/public_html/html/modules/Your_Account/index.php on line 838

When I'm logged in as an administrator, if I click anything at all I get logged back out.

Some additional information that may be of use:
OS: Linux
Kernel version: 2.4.27-grsec
Apache version: 1.3.31 (Unix)
PHP version: 4.3.9
MySQL version: 4.0.22-standard

The site is located at http://www.trekdatabasestorage.info/v2/