Last two days, Sonar will not restart after closing the program

To explain, if I close Sonar Platinum (latest build) the normal way, and then try to reopen it, it doesn't open. Doing a ctrl-alt-delete and going into the task manager reveals that the Sonar is still and open process. If I hit end process, then I can open Sonar again. This is new behavior.  This just started after I used Melodyne Editor 4 for the first time since upgrading it a while back. That's the only thing that I can think of that is different. And it seems like now Melodyne is crashing Sonar when I try to create a region effect, although that worked fine yesterday.  But the close/unable to reopen without ending the process in Task Manager began a couple of days ago, I believe, and I've never had this, or any other problem with this latest Sonar build, which I have had since release and is up to date.
I am running Windows 7 Professional, BTW. No other changes or additions/subtractions to my system, which is dedicated to audio production only (with only occasional internet useage.
Thanks.

I used to have this problem with an older version of Sonar intermittently, and what was worse, trying to use the end process command usually wouldn't work and I had to reboot the computer. I found out it was being caused by my MIDI keyboard drivers. Powering off my MIDI keyboard would allow sonar.exe process to close and I could restart Sonar normally.

Jut did the recent update, seems to have resolved the crash. I meant to,say that I went from melody do editor 2 to Studio 4 when it was released, but hadn't really used it until a couple of days ago, so this was something new. The update of studio 4 I did today resolved the crash when using it.