Been outta the loop for abit. Might be missing something simple but I've opened up a midifile and want to add a vocal. As I insert an audio track I can still hear the midifile playback. When I click to record the audio I can't hear the midi tracks. I can hear my vocal signal coming through. That's as far as I get and then have to close X3 and startup again to hear the midifile. Suggestions? 

What are you using to play the MIDI file? 

I've imported the midifile into X3, just like a regular project. That's what's playing back the midifile. 

Is it possible that both the midi track and the audio track are record enabled ? 
 
This would cause the midi track to go silent.

At this time, any midifile I play results in the same thing. I can hear the midifile play but as soon as I click the audio track record ... all the midifiles are silent. I can't reverse that unless I close X3 and start again. Then I can hear the midifile again.

dotonemanband
I've imported the midifile into X3, just like a regular project. That's what's playing back the midifile. 

What is the midi track output set to?

A MIDI file or just MIDI can't play without going to a synth of some sort. It is not audio but data that tells a synth what note to play at what time. If you imported a MIDI file and did not set up a synth it is most likely using the MS built in synth. Which is the single worst sounding synth there is. This also means you probably are using MME as your audio driver and that is a poor choice. Use ASIO or WDM if you have a proper audio interface.   
 
Load the TTS-1 synth via the browser and make sure that all the outs of the MIDI tracks are going to it. 
 
Also try not to import a MIDI file but load it as a project. MIDI is a native file format for Sonar. When import it it will not use its own tempo but the tempo of the opened project you imported it into. 

I think you'll find John has the answer. If the MIDI tracks are using the MS wavetable that will create all sorts of problems.
 

Thanks for assistance John. You suggest ... Load the project, not import it. So I open X3, go to File-Open-and select midifile from a folder. That opens the midifile in X3.The midifile sounds ok and tempo seems correct. That is what I've done all along. But I'm not sure how to ... "Load the TTS-1 synth via the browser and make sure that all the outs of the MIDI tracks are going to it." Something else. When I checked the midi output in each track, it was showing Microsoft gs wavetable synth and I can hear the file. When I change the midi output to my (cakewalk ua-25ex) interface, then everything goes silent even though I can see the playback levels. I know I'm close but what to do now? 

Is the UA-25ex connected to a MIDI keyboard or MIDI sound module? If it's not, there is no synth to play the MIDI.