Assuming you see no reply box at the bottom of any page including this one then post a new thread in tech support including what platform, OS, browser, etc you are using.
I have just tested the current page incognito (private mode) on chrome and there is no box to reply as the site sees me as not signed in. This could be your issue, are you actually signed in or browsing private mode when trying to reply as it will not allow you to do so, you need to be signed in. if you are signed in properly then it could be a cookie / settings issue. Post in tech support if so.