All we can do here is help you verify the MIDI is working on the 1818. Configuring Ableton is going to be something you'll want to take up with their reference manual and/or their support team.
But here's a quick test to determine if the MIDI data is passing in to Ableton from your 1818.
Once you have a MIDI cable running from the MIDI out of your Yamaha to the MIDI in of the 1818, and you have the 1818 selected as your audio device in Ableton, try this:
-Open Ableton
-Look at the MIDI monitor in the top right hand corner of the screen
-There are two small boxes next to where it says MIDI, one of them should illuminate when you press keys on your keyboard
If you do NOT see any activity there then there is a problem with either the MIDI cable, the keyboard, or possibly the 1818 (but I have never seen a broken MIDI port on an AudioBox 1818).
If you DO see activity, then you've made an error in your configuration and will need to consult your Ableton manual or contact their support team.
