Weird issue…I have a number of songs (30 at present) I am working on for multiple album releases to come in 2016. One and ONLY one of the songs simply will not put out audio. I see the track levels in the MixConsole, the Project Window cursor moves. I have gone to the VST connections Audio Input, Audio Output and Control Room tabs and changed, re-changed, re-re-changed the settings to copy the exact settings that all of the other songs I am working on have (and the rest of them work perfectly) - and I get nothing. This is the only song that has this issue - and its maddening. No individual track will play in solo mode, no combination will either. PC system, all updated to date (Jan 21, 2016), 32G of RAM, big-ole fast hard drive.
A thought…
Any possibility of mute automation on the main stereo out track?
Regards. 
Thanks for the idea, Prock - but no: I actually was about to start automating the mix so no automation info had been sent to the stereo out. It wouldn’t be so weird if ANY of my other tunes had this problem, but ONLY this song does. I have removed and reloaded the VST connections, turned off and on both the A/D convertors (Mackie ONYX), rebooted the computer, arggghhh!
Sorry you are still having issues. Hopefully others will chime in here to assist. 
PIA I know but the only other suggestion I will mention is for you to export a few tracks to a new project and see if they play correctly. If yes… then keep exporting and chalk this up to a corrupted .cpr file.
Good luck and please post how you get this sorted. Thanks.
Regards
thanks again, PRock. I actually had tried that early on, exporting the whole thing, exporting just a few in to a blank project. It might be time for a phone call to Steinberg, I s’pose…thanks anyway!