MyBB Community Forums

I can't log in on my forum. It says I'm logged in at first and then takes me to the index and I'm logged out again.

Site: LightForums.org

I need some help. Thank you.

http://docs.mybb.com/1.8/faq/login/

Your cookie domain is incorrect.

You'll have to edit $settings['cookiedomain'] in inc/settings.php in accordance with the advice in that Doc page, then go to your ACP > Configuration > Settings > General Configuration and change Cookie Domain to the same value.