Reply to an answer

There are two possibilities:

1. If it won't send at all, that would probably be because you haven't completed the 'captcha' text at the bottom (the mixture of lower case and upper case letters).
2. If you have done that and hit save, then you have probably sent it correctly, however to help limit spam new topics are posted straight away but replies have to be checked and released individually by a moderator, so it will appear when that has been done.