Need help with the following: Warning: Cannot modify header information

The domain is stocktradinginvestment[dot]net. When I attempt to go to stocktradinginvestment[dot]net/wp-admin, I get the following error:

Warning: Cannot modify header information - headers already sent by (output started at /home1/bestgpts/public_html/stocktradinginvestment/wp-content/plugins/tubepress/classes/net/php/pear/HTTP/Request2/Adapter.class.php:297) in /home1/bestgpts/public_html/stocktradinginvestment/wp-includes/pluggable.php on line 850

I have very little programming experience. I've tried to figure this out for 4 hours and am ready for some help.

Can someone fix this for me?

By the way, this is how the site should look:

 

Try using ob_start(); function or disable tubepress plugin. By the way, looks like plugin is not working properly

 

As flakas123 said try to turn off tubepress via Admin->Plugins

 

First step would be to make sure that there is no blank line as the last line of the scripts.

 

Are you using any template or did you make any changes to default pages?

The error comes when there are "spaces" at the beginning or end of PHP pages, so make sure as suggested by maestria

'NO SPACES HERE'<?php
.
.
.
. //all the code
.
.
.
.
.
?>'OR HERE'

Code (markup):

 

as said..90% of such errors are caused when blank spaces are left at the start or end..remove them..
thanks

 

ob_start();

at the top fixes such errors