If you are having an issue where you can't stay logged in, this is 99.9% time because your browsers' security level settings are set to a High level.
1) Ensure that your browser supports cookies; if so, check the security level you are using. High levels of security restriction in certain browsers will automatically reject cookies. In order to use the key features of these forums, you'll need to accept cookies. The maker of your browser can help you with additional problems you may have with your cookie settings.
2) Completely log out by hitting the Log Out link in the upper right-hand corner of the page, and then log back in again.
3) After logging in, you may have to hit the Reload or Refresh button on your browser to expedite the authentication.
4) If these steps don't work you can try purging your cookies for this site using the My Cookies tool: My Stuff > Cookies > Expire Cookies