need help with URI

[eluser]mousavi[/eluser]
hi, I’m just starting to use CodeIgniter and I have a problem with segment based URLs.
It doesn’t work when I type my URI. Actually I get HTTP 404 error, even if my $config[‘enable_query_strings’] is set to FALSE in config.php. But when I set it to TRUE the URL works in query string manner.
what can I do? If anybody help, I will be thankful.