are you referring to a site at wordpress.com and your domain was pointed to that site? If so, when your domain expired you lost all the settings. I'm not sure how to set it up, but you have to go to your domain registrar and reconfigure it to point to your wordpress.com site again. I believe you have to set the CNAME or "A" record, something like that. Wordpress.com should provide full instructions.
Note that it may take up to 48 hours for the settings to take hold (propagate over the internet), so make absolutely sure it's properly set up, then wait and see. Hope this helps.