by Howard Miller.
Moodle won't work without a Moodledata folder - so I imagine that there is a bit more to that story!
Switch on Debugging. As you can't get to the admin screens you will need to copy the relevant lines (in Section 7) from config-dist.php to your config.php.
Reproduce the error - are there any errors or warnings displayed? You may need to check your web server's error log.