wp_cron name lookup timed out

Hi all,
sorry for the stupid question, but I don’t know how to solve it.

I have a wp blog using a heavy-modified-by-myself theme which works fine. I added two small functions to functions.php (in the theme) in order to erase some posts at a given time and scheduled them with wp_schedule_event.

When I worked locally (with a copy of my theme) all is fine but on my website server crontrol gives me this message:

There was a problem spawning a call to the WP-Cron system on your site. This means WP-Cron jobs on your site may not work. The problem was:
name lookup timed out

Well, ok… I thougth it was not an important issue so I

1. put
   define('DISABLE_WP_CRON', true);
   in my config
2. copy wp-cron.php to my_own_wp_cron.php
3. changed these lines:

   if ( !empty($_POST) || defined('DOING_AJAX') || defined('DOING_CRON') )
         die();

   to these:

   if ( defined('DOING_AJAX') || defined('DOING_CRON') )
           die();

   in my_own_wp_cron.php

4. create a crontab entry that calls my_own_wp_cron.php

But crontrol shows me the same old functions and (worst thing!) my functions don’t work anymore (when I run them from crontrol… I guess because wp-cron is disabled). And, of course, my_own_wp_cron.php is not called (at least it doesn’t seem so… btw, how can I check this?)

If I set
define('ALTERNATE_WP_CRON',true);
in my config, the error message disappear, but no result anyway…

Thanks in advance for your help.

ps. Is there a way to “clear” wp-cron?