A quick FYI since this question often comes up:
If you are having problems staying logged in or problems logging off the forum it is 99% of the time a problem with your internet cookies. You can navigate away from the site, delete the specific site cookies (if you know how) or delete all of them, but do so in this process:
1) Close all your browser windows.
2) Delete the cookie(s)
3) Re-open the browser and navigate back to the site.
This should resolve the problem.