if i go to this part of the forum, the button magically reappears. But if i go to another part, i dont see no button anywhere. same thing with Reply, and quote.
Random guess: You're browsing locked forums/threads?
Moderators/Admins can "lock" sections of the forum. Usually forums are locked if noone is meant to create threads in then. Threads become locked if a moderator consideres the discussion over / problem solved.
In both cases most usual buttons for normal users disappear.