Can't get audio clips to play

I recorded a bunch of vocal tracks, about 20, into take lanes. I have played them back multiple times this evening so I know there is audio in there, (plus I can see it). But all of a sudden, I can't get those clips to play. I've tried muting and un-muting, turned off all effects, copied the clips into a new audio track, then a new project, recorded new audio in the new project which plays back fine, removed volume envelopes, re-installed the audio card driver, Windows Device Manager says the audio card is working properly, I've rebooted twice, even tried playing one of the .wav files from the \Audio folder in Windows Media Player. After all of this I still can't get any of these clips to play. ITunes plays fine. What's going on?
 
P.S. In case this is relevant, the past week or two I've had to turn off all effects very often, even though this project is less complicated than others I've done. When I turn the effects on, I get a popping sound, then bad hiss, and no audio will play. But then sometimes that doesn't happen and I can hear all my audio with its effects. Seems more often than not I have to turn effects off anymore though. 

Well, it turns out what was happening is that dragging multiple takes from one track to another left exactly one take showing muted for some reason, but in reality the entire set of takes were effectively muted. I had to un-mute the supposedly muted take, and then all takes sprang back to life. This happened every time I did it, until finally I decided to record into the target track directly instead of dragging. Yet another example of Sonar's buggy and non-intuitive nature directing how I work.
 
The other issue is still present though. Moving it to a new thread.