WordPress not updating post or disable plugin instead a white page appear

Question

I was working in a local WordPress website, and it works without any problem. Then i uploaded it to a live server as follow:

• Uploaded all my local files and folder to the live server.
• Imported the local DB to Live server.
• Changed the links in the DB from the (localhost) to my (live domain).
• changed the config.php file to connect to the DB.

after doing these steps my web site ( Front-end ) is working great without any problem.

But when i logged-in to my dashboard and tried to do any of the following i got instead a white page appear without any error:

• When trying to disable/activate any plugin.
• When trying to Update any post.
• When trying to publish new page/post.
• When Deleting page/post.

I tried this solutions but didn't solve the problem:

• I disabled all the plugin to see if any cause a conflict.
• I tried to use the default theme instead of my custom theme.

Update:

After enabling define('WP_DEBUG', true); as @s_ha_dum say, I got this :

• Warning: Cannot modify header information - headers already sent by (output started at /......./wp-content/themes/sbr/functions.php:670) in /......../wp-admin/post.php on line 233.
• Warning: Cannot modify header information - headers already sent by (output started at ............/wp-content/themes/sbr/functions.php:670) in /............./wp-includes/pluggable.php on line 896.