Can't open Sonar after crash - need to reboot

What I do is look for the little midi keyboard icon on the task bar. If it is still there then Sonar is not closed completely. Then I open task manager and tell it to end task. Always works. 

Excellent advice and tips from everyone. Most of my crashes are with V-Vocal. I've tried Melodyne but still like the control I have with V-Vocal, possibly I need the paid version of Melodyne. 
 
Thanks for the tip about it likely being the audio interface, because I think that may be correct. I have been using the latest software for my MOTU AVB Ultralite and just today discovered that it seems to work far better with older software with V-Vocal. I did some testing and didn't get a crash using V-Vocal 12x. So I'll continue testing with all soft synths disconnected  and see if that makes it not crash. 
 
Since Cakewalk/Sonar looked like it was possibly going to disappear I figured I might as well revert back to the most stable version, which was 2017.01. V-Vocal was at least workable with that version. So I've gone back to the software version I was using with that and it seems much better.
 
In the past most V-vocal crashes for me were due to me having several RAM hungry soft synths connected. Disconnecting them makes it less likely I'll get a crash with V-Vocal. It appears V-Vocal has a strange way of accessing memory and if it doesn't get it it crashes. My theory is my newer AVB software is likely using more RAM, thus making it more likely to crash V-Vocal and some newer versions of Platinum may use more RAM too.
 
If I get more crashes I have several new things to try before rebooting.

One of the things I dimly recall about using V-Vocal was that I would encounter FAR less crashes if I did smaller number of measures at a time with V-Vocal.  When I did longer stretches through it is when I had most of my issues when using it.
 
And, if memory serves (which is not very well these days), I think I also would commit a given stretch of audio that had been altered with V-Vocal, once I was happy with the changes, so that I wasn't having much running through V-Vocal at a time.
 
So, the overall approach was to use it, in small chunks at a time, and permanently apply the changes as soon as a small chunk's changes were satisfactorily made - that seemed to go a LONG way toward it all remaining more stable (less crashes in the first place).
 
And, you might want to try using each of the methods for getting resources freed up, as noted in the earlier posts, to see which seem the easiest to perform and have the highest success rate to allow you to recover from a crash without having to reboot.  Anything that causes Windows to kill the 'hold' on resources preventing Sonar from restarting seems to do the trick.
 
My own practice was usually to just turn off the audio interface and turn it back on again.  For folks with audio interfaces that required disconnecting and reconnecting a cable, the other methods would work better for them.
 
Best of luck to you, 
 
Bob Bone
 

gmp
 
Yet do you think I can just unplug it's USB cable and plug it back in? 

Probably not. That won't reset the interface, but might cause it to hang, requiring a reboot anyway.
 
One trick that works on MY interface (which doesn't mean it'll work on yours) is to change the buffer size. That seems to reset the interface and bring it back to life if it ever goes silent on me. 

Possibly you guys have had better luck than I have.
But every time I killed Sonar in task manager or every time I unplugged/turned off my interface, hardware device..
The next time I opened Sonar, I received the "No hardware outputs detected".
I would have to go through the whole process of close/restart until my device showed up again.
 
Logging off/logging on was a 2mintue process and I didn't lose any hardware drivers in the process.

YES!! Used to happen to me ALL THE TIME. My USB MIDI keyboard was the problem (AKAI MPK49). Pulling out the USB wire and plugging it back in always allowed sonarpdr.exe to end and restart but it was a pain in the ass. So, I now run that keyboard through my audio interface using 5-pin MIDI wires - no USB connection in use for the keyboard. Haven't had the problem since - about a year now.