Originally Posted by
mrwarp
The access format of the Steam forums were changed. You now must own the game to view/post in the original forums. I have noticed that it disappears for some since the change. Logging into the game, exiting, then going back to the forums should clear that issue up.
Also, it may have dropped you in the new forum "Steam Community Questions", which is viewable and postable by anyone. Check the right side of the page to see if the other forums are still listed there. If not, the above remedy should fix it.