I have a kick drum sample track, it was working fine a few days ago when I fine-tuned the alignment to the actual kick drum.  I just noted that the level meter for that track is showing no output.  Soloing the track verifies no audible output.  The track outputs to my drum bus, the rest of the percussion plays fine on that bus.  I have EQ and a PC4K expander/gate on the Pro channel, the lights on these show that they are processing a signal, but yet no track output.  The waveforms look fine; the clips are not muted.  The track is not muted.
 
I've tried turning off Pro Channel; re-routing to another bus; turning input echo on/off; closing the project and re-opening.  I'm baffled.  Any suggestions?

I just created a new audio track, copied one of the clips from the kick sample track and pasted into the new audio track -- nothing shows up at all in the new track.

Something at the clip level going on?  It's like there's nothing there to copy even though I see it.  (Again, I'm seeing the lights on the ProChannel modules in the original kick sample working like they're processing something.)

Is that clip muted? I bet you muted it by accident. I'm assuming this is an audio track??? 
Also, triple check your signal chain at each gain stage. Something that you overlooked may be causing it. 

CJ

Also check to see if you have a volume envelope in it. More than once I have done something that caused the envelope to "bottom out" and I get no sound. In X1, if you are not specifically on the volume envelope setting, the envelope is kind of hard to see, and it's easy to miss setting on the bottom of the track.

Found it -- there was an Automated Mute envelope on it.  (I had already tried muting and unmuting clips, and there was no volume envelope.)  I'm not sure how this envelope occurred in the track, I had not intentionally placed any envelopes on this particular track.  And I had clicked the Automation Lanes on previously, as my first assumption was it was a volume envelope -- and the only envelope that showed was the default volume setting for the whole track. 

I would have thought the Automated Mute envelope would have shown in the automation lanes, it only showed when I selected Automation from the Drop down in the track display, and even then it didn't show a colored box beside it; but when I selected it there was an envelope set to on; when I deleted the envelope, problem resolved.

I'm still confused, but at least problem solved.  Thanks.