Littlegolden Why there is still a reply text box after changing the permission to create discussions to 'Only Administrator'
While I'm here I might as well answer this... I believe this is intended behavior. When you're logged out, it invites guests to post new answers, which will them offer them the ability to login or register.
Once logged in, the field will either allow you to write inside of it, or show a disabled input if you're not allowed to reply.
If your forum does not allow users to reply, I understand you might want to change the behavior so that users don't mistakenly believe they could reply by logging in or creating an account. This could be changed via an extension. Maybe even to some extent via CSS depending on what you prefer instead.
Feel free to open a new discussion if you'd like to discuss this further.