I've wordpress placed on domain.com
Now I am attempting to install another wordpress on domain.com/sweets/
I submitted everything but when I arrive at the "sweets/wordpress-admin/setup-config.php" path
it shows a webpage in domain.com saying "Not Found"

I suppose it's something related to the .htaccess?

.htaccess of domain.com/.htaccess

# 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]

RewriteCond %{http_host} ^domain.com [nc]
RewriteRule ^(.*)$ http://www.domain.com/$1 [r=301,nc]

</IfModule>

# END WordPress

Moved from comments thread because it seems to possess reduced the problem:

Does the file exist? And therefore are the permissions onto it so that the installer can open it up?

Answer from Asaf: Ok that's just odd, file permissions of wordpress-admin/ folder were 444, place it to 755 and delay pills work... type of strange it redirects towards the parent folder's website though