Redirect all www.xyz.com to www.xyz.com/wordpress?

To redirect http://www.xyz.com/ to http://www.xyz.com/wordpress/ add these rules to your .htaccess file:

RewriteEngine On
RewriteCond %{HTTP_HOST} ^(www.)?xyz.com$
RewriteRule ^(/)?$ wordpress [L]

That answers the first part of your question. The rest of it is totally vague to me.

Hata!: SQLSTATE[HY000] [1045] Access denied for user 'divattrend_liink'@'localhost' (using password: YES)