Howdy from Texas (resolution below)
 
Last evening I closed SONAR after a long session ...upon start up later... I found sonarplt.exe not closed (this has been an issue for a while with previous versions) ...ended that process ...attempted start again... Nothing.

Went back into task manager and found 1 instance of CakewalkStartScreen.exe open ...attempted to end that task ...I cannot ... Windows dialogue box says program running cannot delete file ...closed studio...

Today, attempted to launch SONAR Platinum ... same problem ...only this time there are 2 instances of CakewalkStartScreen.exe  open ...cannot delete either one...

HELP?
 

BTW: I did research the forum using keyword start screen ...nothing
 

Reboot your computer. You should be shutting down your PC at the end of the day anyway.
When killing Sonar, kill the start screen first then Sonar. If that does not work try Sonar first then start screen. Make sure you kill both processes. 
 
However next time it hangs around in memory, don't kill it...  try and find the actual cause....
The issue is either a dodgy plugin or drivers (often the audio interface itself) .
 
Turn off your devices (keyboards, audio interfaces etc) slowly one by one until Sonar quits.
You can rule out problem plugs by starting Sonar in safe mode. Look at 32 bit plugins first.
 
Regardless you should be considering updating all the device drivers and firmware across the board (and running windows update), and updating your plugins, the real issue is some device driver or plugin is hogging Sonar...

turns out Avast antivirus was the culprit... deleted that ...
Many Thanks to Cakewalk Tech Support

As noted in your other thread you could try MSE instead but Avast is a pretty darned good AV. You could just add all your Sonar/Audio stuff to Avast's whitelist.
 
Avast is pretty aggressive in general though so unless you use your DAW to go online a lot MSE is lighter.
 
Also if you DO use Avast learn how to use it and set it up so it isn't doing all sort of crap in the background.
 
One of the most annoying things it does (and that is directly related to audio) is the Avast Sounds thing. That needs to be disabled immediately. However if your projects are hanging on startup it is likely trying to scan ALL your Sonar stuff (thus the hang) and maybe, if you are on the latest versions of Sonar with that ridiculous "phone home" Start Screen AVAST may be viewing it as some kind of malware... and for good reason.
 
Sonar should NOT be automatically phoning home like that. Not amused they did that.
 
You ahve already deleted AVAST but I would have otherwised suggested disabling the Start Screen (which supposedly keeps it from performing the "phone home" crap") to see if that solved the problem.
 
Cheers.

The ONE time I don't mention antivirus damnit ;)

Doktor Avalanche
The ONE time I don't mention antivirus damnit ;)