Wp-login appears White Screen, Error: Cannot modify header information

Now Here is what I have already did to make it work:

1. Disabling plugin from FTP

Which plugin?

1. Switching theme by renaming the selected theme folder
2. Checking for Space after and before,

After and before what?

1. Replacing WP files with fresh download

You stopped too soon. PHP is telling you what problems are occurring and you seem to be ignoring the notices and warnings it is giving you.

Let’s read the first Notice:

Notice: automatic_feed_links is deprecated since version 3.0! Use add_theme_support( 'automatic-feed-links' ) instead. 

Now let’s wrap the line and add some explanatory text to make it easier to read:

Problem: The automatic_feed_links() function is deprecated since version 3.0.

Solution: Use add_theme_support( 'automatic-feed-links' ); instead.

1. Look through the theme and plugin files for a call to the automatic_feed_links() function.
2. Start with the functions.php theme file.
3. Comment out that function call: // automatic_feed_links(). (It may not look exactly like this.)
4. Add a new line below that line.
5. On the new line add: add_theme_support( 'automatic-feed-links' );
6. Test the change to see if the Notice for that problem goes away.

Let’s read the second Notice:

Notice: wp_deregister_script was called incorrectly. Scripts and styles should not be registered or enqueued until the wp_enqueue_scripts, admin_enqueue_scripts, or login_enqueue_scripts hooks. Please see Debugging in WordPress for more information. (This message was added in version 3.3.) in /home/truckgua/public_html/test2/wp-includes/functions.php on line 3012

Now let’s wrap the line and add some explanatory text to make it easier to read:

Problem: The wp_deregister_script() function was called using the wrong hook.

Solution: Scripts and styles should not be registered or enqueued until the wp_enqueue_scripts, admin_enqueue_scripts, or login_enqueue_scripts hooks.

1. Look through the theme and plugin files for a call to the wp_deregister_script() function.
2. Start with the functions.php theme file.
3. Once you find the line with the wp_deregister_script() function call on it look for the name of the user defined function that line is located in.
4. Now, look for the add_action() function call that points to the user defined function.
5. Comment out that line as you did above.
6. Add a new line below that line.
7. On the new line add: add_action( 'wp_enqueue_scripts', 'the_name of the user defined function' );.
8. Replace the_name of the user defined function with the name of the function you found in user defined function you found in step 3.
9. Test the change to see if the Notice for that problem goes away.
10. If the Notice remains, replace ‘wp_enqueue_scripts’ with ‘admin_enqueue_scripts’ in step 7 and repeat steps 8 and 9.
11. If the Notice remains, replace ‘admin_enqueue_scripts’ with ‘login_enqueue_scripts’ in step 7 and repeat steps 8 and 9.

Once the all Notices are gone, there will no longer be anything added before the headers and the other Warnings may go away.

These changes may not fix the page. Other errors may be doing that, but the Notices should be fixed first, before continuing with more debugging.