ScottStrat
One more question that might be important.  When I check the ASIO panel in audio preferences, under the usb tab there is no device listed.

Very, check if your audio interface is showing up in device manager...windows may have lost it.

Jimbo 88
Hey I just had this same problem.  It was pro channel and the concrete limiter on a master bus.
 
I turned the Pro Channel off and audio would go thru.  Deleted the Concrete limiter and everything was totally fine.
 

Now that looks to be a likely suspect.  I'll try it as soon as I get home.

I've had a similar issue in the past. Is your interface set to be your default soundcard in windows? If it is, try setting your on board card to be the windows default soundcard.
 
Rocky

Shambler

ScottStrat
One more question that might be important.  When I check the ASIO panel in audio preferences, under the usb tab there is no device listed.

Very, check if your audio interface is showing up in device manager...windows may have lost it.

I would have thought the reinstall would have covered that.

ScottStrat

Shambler

ScottStrat
One more question that might be important.  When I check the ASIO panel in audio preferences, under the usb tab there is no device listed.

Very, check if your audio interface is showing up in device manager...windows may have lost it.

I would have thought the reinstall would have covered that.

Does it show up in device manager as installed and working ok?

Bring up your midi preferences and uncheck the "zero controllers when play stops" box.

John
Are your speakers on? Are the meters working?

A little off topic. but a friend of me who runs Pro Tools HD had a problem with his rig one day. He couldn't get any sound from his system. 
He tried everything. He even opened up his Mac to see if the HD pci cards were in place but  with no luck.
Then he looked at his speakers, and they were off

Have you checked the Sample Rate? I once had a similar issue and the tracks did not appear until the Sample Rate was setup properly.

Same kind of problems with the internal soundcard ans ASIO4ALL...I solve the problem by opening ASIO4ALL control panel and validating it.I get a dropout and everything works fine after that.
So try to open the ASIO panel and change settings.

I GOT IT!!!!
 
It was the AudioBox driver.  I ended up going on the PreSonus website and following their "uninstall/install" instructions.  Had to jump through some hoops and manually delete a bunch of files.  My previous attempts at installation had been bogus. 
 
Shambler gets the grand prize for getting me to look at the driver more closely.  I just assumed since other music sources were playing ok that the driver was ok..............not.  On the plus side, I learned a lot more about Sonar and the Audiobox from the experience.  I'm just glad I wasn't up against a dead line.  I'm still curious how I screwed up the driver in the first place..........probably never know. 
 
MANY THANKS TO EVERYONE!!!!!  You all have a great (and helpful) board here, think I'll stick around.
 
Best regards,
Scott