jdenio
I started with a midi sequence and removed all events except notes. And still get no sound from it. Any ideas?

Wrong Midi Channel ?

Did you inadvertently install the 32 bit version? 

Nope to the midi channel, and Nope to the 32bit version

If the synths work with MIDI files supplied by Cakewalk (or when played interactively) and not from third party MIDI files, the problem is the third party MIDI files. A typical symptom of a file with non-note instructions is all the sfz engine synths (DimPro, Rapture, SI series) fail but the other synths work fine. Once the file is played and the sfz engine synth encounters the offending instructions, the sfz engine shuts down. Even after the instructions are removed, the only way to get the synth to play is restart the project. Editing the data from the files in the Event view before playing should resolve the problem. Another way to filter the files, without editing them, is the MIDI Event Filter MFX on each MIDI track. This solution would not work with instrument tracks.

One more thing about controller 7 - a common scenario is a MIDI file that uses controller 7 to fade the level down to 0 at the end of a song. The synth is left in that state until a new controller 7 value comes along to change it. That's why you want to have an initialization at the start of the file. I'm not saying that's definitely what's happening in your case, but it's easy enough to check out and find out if that's the issue.

I just had another quirky relative situation happen. I opened an old project that has 4 instances of the DP 1.5 Synth inserted. Some of the instruments, i.e. Bass and Piano are working but not my string and horn sections. This did work when I created the project... now 2 softsynths work and 2 do not... all of them are DP 1.5 synths. BAZAAR!!!

It's not a matter of midi files supplied by cakewalk and third party files. It's files that I created, that worked, now do not.

jdenio
It's not a matter of midi files supplied by cakewalk and third party files. It's files that I created, that worked, now do not.

Was record EVER turned on between the time you created the sequences and you started having these problems? If so, and you turned down the volume while it was recording, you can be missing that controller 7 maximum level initialization.
 
Do you know how the event list works? That could give some very valuable clues.

"Was record EVER turned on between the time you created the sequences and you started having these problems? If so, and you turned down the volume while it was recording, you can be missing that controller 7 maximum level initialization."
 
No, these are files that were complete, that I had mixed down and created finish product. They worked... now they don't. 

Then you have to figure out what changed between when they worked and when they didn't work. We really don't have much info to go on, except that you re-installed Sonar for some reason thinking that would solve the problem. But the problem may not have been Sonar. You may think you haven't made any changes to your system, but there could have been a Windows update, a piece of spyware, an automatic graphics card update...who knows.
 
I don't think anyone else has experienced this issue, so it's extremely likely it's something a) involving your system, and b) not involving Sonar, because re-installing it didn't help and at one point it worked as expected. We didn't know anything about your system.
 
Just to humor me, could you try inserting a controller 7 value close to the beginning of the sequence on any channels that have instruments? At this point I doubt it will make a difference, but a couple minutes could at least eliminate that option.