The software I use is free to download, and has an extensive online handbook and forums that can help you figure out how to use it. It's called "Musescore." The playback sounds pretty awful compared to Finale or Sibelius software, but it does everything you need to write your music down and it's free. Since you've tried some instruments in the past, but never stuck with it, I wouldn't go out and buy a bunch of expensive software just yet. But learning to write down your tunes can help you learn to read music better, and maybe you'll decide to pick up some music lessons again too. First step is always to just get started. (: