Help! Kontakt makes no sound in Sonar Platinum

Make sure it's up to date in NI service center.
You could try a VST reset and then rescan in Sonar preferences to see if it makes a difference..

Otherwise check the ultimate kontakt thread, maybe something will help:
http://forum.cakewalk.com...aspx?m=3030422&p=1

Are you using a simple instrument track, or a separate audio and midi track for assign things to route to and from Kontakt?
 
And, as asked above, please detail your input and output routing assignments for your tracks, as well as the midi channel that your midi track is set to use, (or omni), as well as the midi channel that your Session Horns instrument is set to in the Kontakt instance.
 
Additionally, is your midi track set to midi input echo on?  By default, this will happen automatically in Sonar if you click on the midi track associated with that Kontakt instance with the Session Horns instrument loaded, to bring that midi track into focus (you will see that midi track's Track Number light up, and that should also automatically turn that midi track's midi input echo on button to blue).
 
If you are using a separate audio track and separate midi track you should have things set up to have:
 
1)  An instance of Kontakt, with a Session Horns instrument loaded.  Check the Midi Channel that this Session Horns instrument instance is set to respond to, by looking at its setting in Kontakt.  
 
2) An Audio Track with its Input set to receive the Output from the Session Horns instrument from that Kontakt instance.
 
3).  A Midi Track with Input set to its default (Omni or None, or a particular midi controller if you want to specify one), and its Output set to the instance of Kontakt that has your Session Horns instrument loaded.  PLEASE NOTE that if the Kontakt instance of Session Horns is set to respond to any midi channel other than 1, that you EITHER need to change that back to midi channel 1, OR you need to also set the Midi Output Channel for that midi track to the same midi channel.  (you will find that parameter on the midi track channel strip, just below the F/X bin, and you can click on the drop down arrow for that and select the matching midi channel).
 
4).  You then want to EITHER click on that midi track to bring it into focus, which should then automatically set that midi track's input echo on button to On, OR you can manually click that track's midi input echo on button to On, which will turn that button blue.
 
5.  If the above is all set properly, playing a midi controller should result in sound,  as long as the note numbers you are playing on the controller are within the instrument's range (a super low E won't play for most sampled violin instruments, for example).
 
I hope the above makes some kind of sense, AND that it helps, 
 
Bob Bone