It usually tells you if you have not put a title and will not accept your thread without one. So if you clicked on to the submit button before you found a title for your thread it would just disappear. You will have to do it again.
A post more than a couple of lines is best done in a memo program on your computer, something like Wordpad or Notepad. You can then easily copy it into the AB window. This method is also very handy when there is intermittent internet connection, either at your end or at AB. If you use MS Word you can even do a quick spell check if you're so inclined.