"Starting a bit over a week ago..." Were things working before then, or not?
I feel your pain but for future reference, I highly advise against messing with the registry, uninstalling/reinstalling, deleting old versions, etc. The reality is that if there was some kind of universal SONAR problem like what you're experiencing, there would be people with pitchforks and torches outside the Cakewalk offices. Platinum simply refuses to crash for me (thankfully), and that should be the norm.
If everything worked up to a certain point you have to consider what might have changed. It could be a Windows update (unlikely), it could be installing something that overwrote a component used by SONAR. It could be a RAM stick failing. The first thing to do would be to roll back to a System Restore point when things were working and take it from there.
Good installation routines will set a system restore point automatically as part of the installation process, but not all programs do. I always set a system restore before installing anything, and set restore points periodically. And it's a good thing - the last Windows update made it impossible to read certain USB devices that had always worked perfectly. The next day there was another Windows update, and everything worked again. Go figure.
People often assume that if they're having a problem with SONAR, it must relate to SONAR. While that can be the case for more subtle issues, if you're having a crashathon every time you open the program, it's probably not the program but something system related.