Site redirecting to http://example.com/wp-signup.php?new=example.com

I’d check the htaccess file to see if is like the recommended one by WP:

# 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

(See https://codex.wordpress.org/htaccess )

I’d also check the ‘options’ table for the two instances of the site root domain (something like http://www.example.com ). Check that also in the admin Options, General page.

You could also use Firebug debugger in Firefox: use the “Net” tab to see the requests made on loading the page. Click on the first entry and then look at the “Response” tab for possible clues.

Good luck!