Warning: session_start(): Cannot send session cookie, cache, modify header infor

Hi all of a sudden this morning i open my website and i get two errors at the top and also the menu and logo are hovering when i scroll and site is messed up in general.

Warning: session_start(): Cannot send session cookie – headers already sent by (output started at /home/mbeste/public_html/wp-load.php:1) in /home/mbeste/public_html/wp-content/themes/enfold/config-templatebuilder/avia-shortcodes/masonry_entries.php on line 32

Warning: session_start(): Cannot send session cache limiter – headers already sent (output started at /home/mbeste/public_html/wp-load.php:1) in /home/mbeste/public_html/wp-content/themes/enfold/config-templatebuilder/avia-shortcodes/masonry_entries.php on line 32

On home page if i try and click one of the THUMB images below like Jewellery, textiles, rings etc i get a blank white page with an extra error:
Warning: Cannot modify header information – headers already sent by (output started at /home/mbeste/public_html/wp-load.php:1) in /home/mbeste/public_html/wp-includes/pluggable.php on line 1196

The only thing i did since yesterday is that i installed the WP-Piwik but the site was fine after that for one day.
Now on back-end if i click on Dashboard the WP-Piwik i get lots of WARNINGS.

I deactivated the WP-Piwik but i still get the same errors. And when i activate it again i get:
Warning: Cannot modify header information – headers already sent by (output started at /home/mbeste/public_html/wp-load.php:1) in /home/mbeste/public_html/wp-includes/pluggable.php on line 1196

Also when i visit my piwik stats
http://mysite.com/analytics/piwik/ i get:
Fatal error: Namespace declaration statement has to be the very first statement in the script in /home/mbeste/public_html/analytics/piwik/plugins/VisitFrequency/VisitFrequency.php on line 9

i tried some solutions found here in forums like adding the below line on bottom of functions.php but i get fatal error.
add_theme_support(‘avia_no_session_support’);
So i removed it

I was trying to create a new User so i can send you a Private Content Link, so i logout of back end and now is not letting me Loggin anymore.
When i go to my site.com/wp-admin/ i get:
Warning: Cannot modify header information – headers already sent by (output started at /home/mbeste/public_html/wp-load.php:1) in /home/mbeste/public_html/wp-includes/pluggable.php on line 1196

Please Help

Thank you