If you have moved the site to a different server or even just a different domain name the problem might be in the site settings in the entry for the default portal alias. But if the site is not loading, you must edit the data in the PortalSettings table to alter the settings.
In the PortalSettings table, find the record for your portalID (probably 0 but maybe not) where [Settingname]= DefaultPortalAlias. Clear the value on this record.
Then find the record for PortalAliasMapping for the same portalID and if it is Redirect change it to CANONICALURL. Save the record and you might have to restart the application pool or touch (edit) the web.config to cause a site restart.