500 internal server error on admin page after moving from subdirectory to root

I moved my wordpress site from a subdirectory (/new) to the root folder, following this tutorial http://code.tutsplus.com/tutorials/moving-wordpress-moving-your-site-from-a-subdirectory-to-the-root-directory–cms-22848

everything works fine: the website is now accessible from the main domain http://www.gogolandcompany.com/, even if wordpress is still in the /new subdirectory.

when I try to access http://www.gogolandcompany.com/admin to access my dashboard I get redirected to http://www.gogolandcompany.com/new/wp-admin/ and get a 500 internal server error.

things I already tried and didn’t work: deactivated and reactivated all my plugins, Increased the PHP Memory Limit.

Could it be a problem related to .htaccess file?
I have now 2 different .htaccess file.
one is in the root directory with this code:

# BEGIN WordPress
<IfModule mod_rewrite.c>
RewriteEngine On
RewriteBase /
RewriteRule ^index\.php$ – [L]
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule . /index.php [L]
</IfModule>

# END WordPress

then I have a second .htaccess file in the /new subfolder

# BEGIN WordPress
<IfModule mod_rewrite.c>
RewriteEngine On
RewriteBase /
RewriteRule ^index\.php$ – [L]
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule . /index.php [L]
</IfModule>

# END WordPress

If I delete only this second one (in the /new subfolder) nothing changes:
– website works in every page
– admin page return 500 internal server error

If I delete only the .htaccess file in the root, this happens:
– homepage still works
– every other page of the website returns 404 not found
– admin page returns 404 not found

I have the feeling that this has something to do with Permalinks but I cannot enter my dashboard.
any help will be welcomed! I finished my ideas and this is my first wp experiment!
thank you very much